Phase C: Add Manual Journal Entries (double-entry GL)

- JournalEntry + JournalEntryLine entities with Draft/Posted/Reversed lifecycle
- JournalEntryStatus enum (Draft, Posted, Reversed)
- Migration AddJournalEntries: two new tables with self-referencing reversal FK
- IUnitOfWork/UnitOfWork wired with JournalEntries + JournalEntryLines repos
- ApplicationDbContext: DbSets, tenant query filters, reversal FK config
- LedgerService: JE lines added as 10th source in GetAccountLedgerAsync and ComputePriorBalanceAsync
- JournalEntriesController: Index (All/Draft/Posted tabs), Create, Details, Post, Reverse, Delete
- Views: Index, Create (dynamic balanced line grid with running debit/credit totals), Details
- journal-entry-create.js: dynamic line management with balance indicator
- Nav: Journal Entries added to Finance section in _Layout

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

src/PowderCoating.Core/Interfaces/IUnitOfWork.cs

@@ -91,6 +91,10 @@ public interface IUnitOfWork : IDisposable
     IRepository<BillPayment> BillPayments { get; }
     IRepository<Expense> Expenses { get; }
 
+    // Manual Journal Entries
+    IRepository<JournalEntry> JournalEntries { get; }
+    IRepository<JournalEntryLine> JournalEntryLines { get; }
+
     // Notifications — typed repository for IgnoreQueryFilters-based history lookups
     INotificationLogRepository NotificationLogs { get; }
     IRepository<NotificationTemplate> NotificationTemplates { get; }