Add workspace DDL lock env var and maintenance mode UI (#19130)

## Summary

- Add `WORKSPACE_SCHEMA_DDL_LOCKED` env-only boolean config variable
that blocks all workspace schema DDL changes when set to `true`. This is
intended for hot upgrades where logical replication cannot handle DDL
changes. Enforced at two chokepoints:
- `WorkspaceMigrationRunnerService.run` — blocks all metadata-driven DDL
(object/field/index CRUD, app sync/uninstall, standard app sync, upgrade
commands)
- `WorkspaceDataSourceService.createWorkspaceDBSchema` /
`deleteWorkspaceDBSchema` — blocks workspace creation (sign-up) and hard
deletion. Uses a dedicated `WorkspaceDataSourceException` (not
ForbiddenException)

- Add maintenance mode feature with Admin Panel UI and user-facing
banner:
- **Backend**: `MaintenanceModeService` stores maintenance window
(startAt, endAt, optional link) in `core.keyValuePair` as
`CONFIG_VARIABLE`. Validates endAt > startAt. Uses `GraphQLISODateTime`
scalar for date fields. Exposed via `clientConfig` REST endpoint and
admin GraphQL mutations (`setMaintenanceMode`, `clearMaintenanceMode`)
- **Admin Panel**: New "Maintenance Mode" section in Health tab with UTC
datetime pickers and activate/deactivate controls
- **Banner**: `InformationBannerMaintenance` displayed at the top of
`DefaultLayout` for all users, using Temporal API for timezone-aware
formatting with an optional "Learn more" link

These two features are **independent** — the DDL lock is controlled via
env var for operational use, while maintenance mode is a UI notification
mechanism controlled from the admin panel.

packages/twenty-server/src/engine/workspace-manager/workspace-migration/workspace-migration-runner/exceptions/workspace-migration-runner.exception.ts

@@ -8,6 +8,7 @@ export const WorkspaceMigrationRunnerExceptionCode = {
   INTERNAL_SERVER_ERROR: 'INTERNAL_SERVER_ERROR',
   EXECUTION_FAILED: 'EXECUTION_FAILED',
   APPLICATION_NOT_FOUND: 'APPLICATION_NOT_FOUND',
+  DDL_LOCKED: 'DDL_LOCKED',
 } as const;
 
 const getWorkspaceMigrationRunnerExceptionUserFriendlyMessage = (
@@ -20,6 +21,8 @@ const getWorkspaceMigrationRunnerExceptionUserFriendlyMessage = (
       return msg`Migration execution failed.`;
     case WorkspaceMigrationRunnerExceptionCode.APPLICATION_NOT_FOUND:
       return msg`Application not found.`;
+    case WorkspaceMigrationRunnerExceptionCode.DDL_LOCKED:
+      return msg`Workspace schema changes are temporarily locked.`;
     default:
       assertUnreachable(code);
   }

packages/twenty-server/src/engine/workspace-manager/workspace-migration/workspace-migration-runner/services/workspace-migration-runner.service.ts

@@ -6,6 +6,7 @@ import { isDefined } from 'twenty-shared/utils';
 import { DataSource } from 'typeorm';
 
 import { LoggerService } from 'src/engine/core-modules/logger/logger.service';
+import { TwentyConfigService } from 'src/engine/core-modules/twenty-config/twenty-config.service';
 import { WorkspaceManyOrAllFlatEntityMapsCacheService } from 'src/engine/metadata-modules/flat-entity/services/workspace-many-or-all-flat-entity-maps-cache.service';
 import { AllFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/types/all-flat-entity-maps.type';
 import { getMetadataFlatEntityMapsKey } from 'src/engine/metadata-modules/flat-entity/utils/get-metadata-flat-entity-maps-key.util';
@@ -35,6 +36,7 @@ export class WorkspaceMigrationRunnerService {
     private readonly workspaceCacheStorageService: WorkspaceCacheStorageService,
     private readonly workspaceCacheService: WorkspaceCacheService,
     private readonly logger: LoggerService,
+    private readonly twentyConfigService: TwentyConfigService,
   ) {}
 
   private getLegacyCacheInvalidationPromises({
@@ -168,6 +170,14 @@ export class WorkspaceMigrationRunnerService {
     metadataEvents: MetadataEvent[];
     hasSchemaMetadataChanged: boolean;
   }> => {
+    if (this.twentyConfigService.get('WORKSPACE_SCHEMA_DDL_LOCKED')) {
+      throw new WorkspaceMigrationRunnerException({
+        message:
+          'Workspace schema DDL changes are locked. This is typically set during hot upgrades.',
+        code: WorkspaceMigrationRunnerExceptionCode.DDL_LOCKED,
+      });
+    }
+
     this.logger.time('Runner', 'Total execution');
     this.logger.time('Runner', 'Initial cache retrieval');