fix: add missing datatable methods to handlers-n8n-manager mock client

CI fails because handlers-manage-datatable.test.ts and handlers-n8n-manager.test.ts
share the same Vitest worker and module cache. The manage-datatable test mocks
N8nApiClient with 20 methods but handlers-n8n-manager only had 10. When running
in parallel, the singleton client state leaked between files causing mock mismatches.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit/mcp/handlers-n8n-manager.test.ts

@@ -100,6 +100,16 @@ describe('handlers-n8n-manager', () => {
       listExecutions: vi.fn(),
       deleteExecution: vi.fn(),
       healthCheck: vi.fn(),
+      createDataTable: vi.fn(),
+      listDataTables: vi.fn(),
+      getDataTable: vi.fn(),
+      updateDataTable: vi.fn(),
+      deleteDataTable: vi.fn(),
+      getDataTableRows: vi.fn(),
+      insertDataTableRows: vi.fn(),
+      updateDataTableRows: vi.fn(),
+      upsertDataTableRow: vi.fn(),
+      deleteDataTableRows: vi.fn(),
     };
 
     // Setup mock repository