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.Infrastructure/Repositories/UnitOfWork.cs

@@ -142,6 +142,10 @@ public class UnitOfWork : IUnitOfWork
     private IRepository<BillPayment>? _billPayments;
     private IRepository<Expense>? _expenses;
 
+    // Manual Journal Entries
+    private IRepository<JournalEntry>? _journalEntries;
+    private IRepository<JournalEntryLine>? _journalEntryLines;
+
     /// <summary>
     /// Initialises the unit of work with the scoped <paramref name="context"/>.
     /// The context is shared across all repositories created by this instance so that
@@ -513,6 +517,15 @@ public class UnitOfWork : IUnitOfWork
     public IRepository<Expense> Expenses =>
         _expenses ??= new Repository<Expense>(_context);
 
+    // Manual Journal Entries
+    /// <summary>Repository for <see cref="JournalEntry"/> double-entry manual journal entries; tenant-filtered with soft delete.</summary>
+    public IRepository<JournalEntry> JournalEntries =>
+        _journalEntries ??= new Repository<JournalEntry>(_context);
+
+    /// <summary>Repository for <see cref="JournalEntryLine"/> individual debit/credit lines within a journal entry.</summary>
+    public IRepository<JournalEntryLine> JournalEntryLines =>
+        _journalEntryLines ??= new Repository<JournalEntryLine>(_context);
+
     /// <summary>
     /// Flushes all pending changes in the EF Core change tracker to the database.
     /// Returns the number of state entries written.