Phase G: Add Recurring Transactions (BackgroundService + CRUD UI)

- RecurringTemplate entity with Frequency/IntervalCount/NextFireDate/EndDate/MaxOccurrences/TemplateData JSON
- RecurringFrequency + RecurringTemplateType enums
- RecurringTransactionService BackgroundService: hourly check, creates Draft bills or immediate expenses, advances NextFireDate, auto-deactivates on limits
- RecurringTemplatesController: Index/Create/Edit/ToggleActive/Delete/GenerateNow (on-demand fire)
- Three views + external JS for type-toggle and dynamic bill line items
- Finance sidebar nav: Recurring Transactions
- Migration: AddRecurringTemplates

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Views/Shared/_Layout.cshtml

@@ -1142,6 +1142,10 @@
                             <i class="bi bi-bank2"></i>
                             <span>Bank Reconciliation</span>
                         </a>
+                        <a asp-controller="RecurringTemplates" asp-action="Index" class="nav-link">
+                            <i class="bi bi-arrow-repeat"></i>
+                            <span>Recurring Transactions</span>
+                        </a>
                         if (hasReports)
                         {
                             <a asp-controller="AccountingExport" asp-action="Index" class="nav-link">