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.Core/Entities/Accounting.cs

@@ -286,6 +286,38 @@ public class VendorCreditApplication : BaseEntity
     public virtual Bill Bill { get; set; } = null!;
 }
 
+/// <summary>
+/// A saved recipe for a document that should be automatically created on a recurring schedule.
+/// The <see cref="TemplateData"/> column stores a JSON blob whose schema depends on
+/// <see cref="TemplateType"/>: see <c>RecurringTransactionService</c> for the exact shape.
+/// <para>
+/// Bills are created as Draft so the user can review before posting.
+/// Expenses are created immediately (already-paid transactions).
+/// </para>
+/// Numbering: REC-YYMM-####
+/// </summary>
+public class RecurringTemplate : BaseEntity
+{
+    public string Name { get; set; } = string.Empty;
+    public RecurringTemplateType TemplateType { get; set; }
+    public RecurringFrequency Frequency { get; set; }
+    /// <summary>Every N periods. E.g. Frequency=Monthly, IntervalCount=3 → quarterly.</summary>
+    public int IntervalCount { get; set; } = 1;
+    /// <summary>UTC date when the template will next fire. Set to the desired first occurrence date on creation.</summary>
+    public DateTime NextFireDate { get; set; }
+    /// <summary>Optional UTC date after which no further occurrences are generated.</summary>
+    public DateTime? EndDate { get; set; }
+    /// <summary>Optional hard cap on total occurrences. Null = unlimited.</summary>
+    public int? MaxOccurrences { get; set; }
+    /// <summary>How many documents have been generated so far.</summary>
+    public int OccurrenceCount { get; set; }
+    public bool IsActive { get; set; } = true;
+    /// <summary>JSON payload whose schema matches the TemplateType. See RecurringTransactionService.</summary>
+    public string TemplateData { get; set; } = "{}";
+    /// <summary>Last error from the background service, cleared on next successful fire.</summary>
+    public string? LastError { get; set; }
+}
+
 /// <summary>
 /// A named tax rate (e.g., "CA Sales Tax 8.25%") used to pre-fill the TaxPercent field on
 /// invoices when a taxable customer is selected. Companies can define multiple rates for