feat: Implement new General Ledger frontend section with comprehensive report screens and cash/bank account management

- Added a new Ledgers sidebar section for statutory-format financial reports and cash/bank-account management.
- Introduced dedicated GL client for API interactions, handling response envelopes and error management.
- Developed report screens for Trial Balance, Balance Sheet, General Ledger, Profit & Loss, Cash Flow, Budget vs Actual, and a new Tax Report.
- Implemented CSV download functionality alongside existing PDF downloads for all report screens.
- Separated Cash and Bank accounts into distinct tables/endpoints, with updated create forms and unified list view.
- Created a new Accounts section for Cheque Management, moving Cash/Bank Accounts from the Ledgers section.
- Updated RBAC navigation to include new permissions and sub-navigation items for the added features.
- Ensured compliance with GL's updated API contract, including renaming fields and adjusting response shapes.
- Addressed various bugs and presentation issues, enhancing user experience across the new module.

Backend/ERPCore/System/Errors/ErrorCodes.cs

@@ -66,4 +66,7 @@ public static class ErrorCodes
     public const string LeftoverExceedsConsumed = "LEFTOVER_EXCEEDS_CONSUMED";
     public const string RunCostClosed = "RUN_COST_CLOSED";
     public const string RunNotCancellable = "RUN_NOT_CANCELLABLE";
+
+    // General Ledger service proxy (GeneralLedgerController → external GL service, docs/12)
+    public const string GlServiceUnavailable = "GL_SERVICE_UNAVAILABLE";
 }