Add sales tax remittance flow

Audit finding #4: Sales Tax Payable was credited on every invoice but never
relieved (no remittance flow), so the liability grew forever. Adds a dedicated
"Record Sales Tax Payment" action that posts a balanced journal entry — DR Sales
Tax Payable (2200) / CR the chosen bank account — honoring the period lock.

Implemented in JournalEntriesController (reuses its posting + numbering + period-
lock infrastructure): a GET form showing the current 2200 liability and a bank
picker, and a POST that creates the posted JE and updates balances. Reachable via
a "Record Payment" button on the Sales Tax report. No reporting changes needed —
posted JE lines are already accounted for across the trial balance / balance sheet
/ ledger. Build clean; 284 unit tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Web/Controllers/JournalEntriesController.cs

@@ -196,6 +196,105 @@ public class JournalEntriesController : Controller
         return RedirectToAction(nameof(Details), new { id });
     }
 
+    // ── Sales Tax Remittance ───────────────────────────────────────────────────
+
+    /// <summary>
+    /// Form to record a sales tax payment to the tax authority. Shows the current Sales Tax Payable
+    /// (2200) liability and a bank-account picker. Relieves the liability that invoices accumulate.
+    /// </summary>
+    // GET: /JournalEntries/SalesTaxPayment
+    public async Task<IActionResult> SalesTaxPayment()
+    {
+        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");
+        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
+
+        var taxAcct = (await _unitOfWork.Accounts.FindAsync(
+            a => a.CompanyId == companyId && a.AccountNumber == "2200" && a.IsActive)).FirstOrDefault();
+        ViewBag.TaxLiability = taxAcct?.CurrentBalance ?? 0m;
+        ViewBag.TaxAccountFound = taxAcct != null;
+
+        var banks = await _unitOfWork.Accounts.FindAsync(a => a.CompanyId == companyId && a.IsActive
+            && (a.AccountSubType == AccountSubType.Checking
+             || a.AccountSubType == AccountSubType.Savings
+             || a.AccountSubType == AccountSubType.Cash));
+        ViewBag.BankAccounts = banks.OrderBy(a => a.AccountNumber)
+            .Select(a => new SelectListItem($"{a.AccountNumber} – {a.Name}", a.Id.ToString())).ToList();
+
+        return View();
+    }
+
+    /// <summary>
+    /// Records a sales tax remittance as a posted journal entry: DR Sales Tax Payable (2200) / CR the
+    /// chosen bank account. Honors the period lock. The reporting already accounts for posted JE lines,
+    /// so this is all that's needed to relieve the liability.
+    /// </summary>
+    // POST: /JournalEntries/SalesTaxPayment
+    [HttpPost]
+    [Authorize(Policy = AppConstants.Policies.CanManageJobs)]
+    [ValidateAntiForgeryToken]
+    public async Task<IActionResult> SalesTaxPayment(decimal amount, DateTime paymentDate, int bankAccountId, string? reference)
+    {
+        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");
+        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
+
+        if (amount <= 0)
+        {
+            TempData["Error"] = "Enter a payment amount greater than zero.";
+            return RedirectToAction(nameof(SalesTaxPayment));
+        }
+
+        var taxAcct = (await _unitOfWork.Accounts.FindAsync(
+            a => a.CompanyId == companyId && a.AccountNumber == "2200" && a.IsActive)).FirstOrDefault();
+        if (taxAcct == null)
+        {
+            TempData["Error"] = "No active Sales Tax Payable (2200) account found in your chart of accounts.";
+            return RedirectToAction(nameof(SalesTaxPayment));
+        }
+
+        var bankAcct = await _unitOfWork.Accounts.GetByIdAsync(bankAccountId);
+        if (bankAcct == null || bankAcct.CompanyId != companyId)
+        {
+            TempData["Error"] = "Select a valid bank account to pay from.";
+            return RedirectToAction(nameof(SalesTaxPayment));
+        }
+
+        var company = await _unitOfWork.Companies.GetByIdAsync(companyId);
+        if (Web.Helpers.AccountingPeriodValidator.IsLocked(paymentDate, company?.BookLockedThrough))
+        {
+            TempData["Error"] = Web.Helpers.AccountingPeriodValidator.LockedMessage(company!.BookLockedThrough);
+            return RedirectToAction(nameof(SalesTaxPayment));
+        }
+
+        var entryNumber = await GenerateEntryNumberAsync(companyId);
+        var entry = new JournalEntry
+        {
+            EntryNumber = entryNumber,
+            EntryDate   = paymentDate,
+            Reference   = string.IsNullOrWhiteSpace(reference) ? "Sales tax remittance" : reference.Trim(),
+            Description = $"Sales tax remittance — {amount:C}",
+            Status      = JournalEntryStatus.Posted,
+            PostedAt    = DateTime.UtcNow,
+            PostedBy    = User.Identity?.Name,
+            CompanyId   = companyId,
+            Lines = new List<JournalEntryLine>
+            {
+                new() { AccountId = taxAcct.Id,  DebitAmount = amount, CreditAmount = 0, Description = "Sales tax paid to authority", LineOrder = 0, CompanyId = companyId },
+                new() { AccountId = bankAcct.Id, DebitAmount = 0, CreditAmount = amount, Description = $"Paid from {bankAcct.Name}", LineOrder = 1, CompanyId = companyId }
+            }
+        };
+
+        await _unitOfWork.ExecuteInTransactionAsync(async () =>
+        {
+            await _unitOfWork.JournalEntries.AddAsync(entry);
+            await _accountBalanceService.DebitAsync(taxAcct.Id, amount);    // reduce the liability
+            await _accountBalanceService.CreditAsync(bankAcct.Id, amount);  // cash leaves the bank
+            await _unitOfWork.CompleteAsync();
+        });
+
+        TempData["Success"] = $"Recorded sales tax remittance of {amount:C} ({entryNumber}).";
+        return RedirectToAction(nameof(Details), new { id = entry.Id });
+    }
+
     // ── Reverse ──────────────────────────────────────────────────────────────
 
     [HttpPost]

src/PowderCoating.Web/Views/JournalEntries/SalesTaxPayment.cshtml

@@ -0,0 +1,72 @@
+@{
+    ViewData["Title"] = "Record Sales Tax Payment";
+    ViewData["PageIcon"] = "bi-cash-stack";
+    var taxLiability = (decimal)(ViewBag.TaxLiability ?? 0m);
+    var taxFound = (bool)(ViewBag.TaxAccountFound ?? false);
+    var banks = ViewBag.BankAccounts as List<Microsoft.AspNetCore.Mvc.Rendering.SelectListItem> ?? new List<Microsoft.AspNetCore.Mvc.Rendering.SelectListItem>();
+}
+
+<div class="d-flex align-items-center gap-2 mb-3">
+    <a asp-action="Index" class="btn btn-sm btn-outline-secondary"><i class="bi bi-arrow-left"></i></a>
+    <h5 class="mb-0">Record Sales Tax Payment</h5>
+</div>
+
+@if (!taxFound)
+{
+    <div class="alert alert-warning">
+        No active <strong>Sales Tax Payable (2200)</strong> account was found in your chart of accounts. Add one first.
+    </div>
+}
+else
+{
+    <div class="row">
+        <div class="col-lg-7">
+            <div class="card shadow-sm mb-3">
+                <div class="card-body d-flex justify-content-between align-items-center">
+                    <div>
+                        <span class="text-muted d-block">Current Sales Tax Payable</span>
+                        <span class="text-muted small">Tax collected on invoices and owed to the authority.</span>
+                    </div>
+                    <span class="h4 mb-0 @(taxLiability > 0 ? "text-danger" : "text-success")">@taxLiability.ToString("C")</span>
+                </div>
+            </div>
+
+            <form asp-action="SalesTaxPayment" method="post" class="card shadow-sm">
+                @Html.AntiForgeryToken()
+                <div class="card-body">
+                    <div class="mb-3">
+                        <label class="form-label">Amount paid</label>
+                        <div class="input-group">
+                            <span class="input-group-text">$</span>
+                            <input type="number" step="0.01" min="0.01" name="amount" class="form-control"
+                                   value="@(taxLiability > 0 ? taxLiability.ToString("0.00") : "")" required />
+                        </div>
+                        <div class="form-text">Defaults to the full balance &mdash; edit if you're paying a partial period.</div>
+                    </div>
+                    <div class="mb-3">
+                        <label class="form-label">Payment date</label>
+                        <input type="date" name="paymentDate" class="form-control" value="@DateTime.Today.ToString("yyyy-MM-dd")" required />
+                    </div>
+                    <div class="mb-3">
+                        <label class="form-label">Paid from (bank account)</label>
+                        <select name="bankAccountId" class="form-select" required>
+                            <option value="">Select an account&hellip;</option>
+                            @foreach (var b in banks)
+                            {
+                                <option value="@b.Value">@b.Text</option>
+                            }
+                        </select>
+                    </div>
+                    <div class="mb-3">
+                        <label class="form-label">Reference / period <span class="text-muted">(optional)</span></label>
+                        <input type="text" name="reference" class="form-control" placeholder="e.g. Q2 2026 sales tax" />
+                    </div>
+                    <div class="alert alert-light border small mb-3">
+                        Posts a journal entry: <strong>DR</strong> Sales Tax Payable / <strong>CR</strong> the chosen bank account.
+                    </div>
+                    <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1"></i>Record payment</button>
+                </div>
+            </form>
+        </div>
+    </div>
+}

src/PowderCoating.Web/Views/Reports/SalesTax.cshtml

@@ -31,6 +31,9 @@
     <a asp-action="Index" class="btn btn-sm btn-outline-secondary"><i class="bi bi-arrow-left"></i></a>
     <p class="text-muted mb-0">@Model.From.ToString("MMM d") &ndash; @Model.To.ToString("MMM d, yyyy") · @(Model.TaxableInvoiceCount + Model.NonTaxableInvoiceCount) invoices</p>
     <div class="ms-auto d-flex gap-2">
+        <a href="@Url.Action("SalesTaxPayment", "JournalEntries")" class="btn btn-sm btn-primary no-print">
+            <i class="bi bi-cash-stack me-1"></i>Record Payment
+        </a>
         <a href="@Url.Action("SalesTaxCsv", new { from = Model.From.ToString("yyyy-MM-dd"), to = Model.To.ToString("yyyy-MM-dd") })"
            class="btn btn-sm btn-outline-success no-print">
             <i class="bi bi-filetype-csv me-1"></i>Export CSV