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/Enums/AccountingEnums.cs

@@ -79,3 +79,14 @@ public enum AccountingMethod
     /// <summary>Revenue and expenses recognised when earned/incurred (default).</summary>
     Accrual = 1
 }
+
+/// <summary>Lifecycle state of a Manual Journal Entry.</summary>
+public enum JournalEntryStatus
+{
+    /// <summary>Not yet posted — can still be edited or deleted.</summary>
+    Draft = 0,
+    /// <summary>Posted to the GL — immutable; can only be reversed.</summary>
+    Posted = 1,
+    /// <summary>A reversal JE has been created and posted for this entry.</summary>
+    Reversed = 2
+}