feat(ai): wire up workspace RAG bulk reindex + manual "Reindex now"

The WORKSPACE_CREATE_EMBEDDINGS / WORKSPACE_DELETE_EMBEDDINGS jobs were
enqueued (on AI Search enable/disable) but had no AI_QUEUE handler, so
existing pages were never indexed ("Indexed 0 of N pages") and disabling
never purged embeddings.

- EmbeddingProcessor: handle WORKSPACE_CREATE_EMBEDDINGS (bulk reindex all
  live pages) and WORKSPACE_DELETE_EMBEDDINGS (purge workspace embeddings)
- EmbeddingIndexerService: add reindexWorkspace() (skips when embeddings
  unconfigured; per-page error isolation) and removeWorkspace()
- PageRepo.getIdsByWorkspace(), PageEmbeddingRepo.deleteByWorkspace()
- AiSettingsService.reindex() + admin-only POST /workspace/ai-settings/reindex
- Frontend: "Reindex now" button, service call and mutation
- Stable per-workspace jobId with remove-before-add so a stale job can't
  block future reindexes; cancel the delayed purge on enable/reindex so it
  can't wipe freshly-built embeddings

apps/server/src/integrations/ai/ai.module.ts

@@ -1,5 +1,7 @@
 import { Module } from '@nestjs/common';
+import { BullModule } from '@nestjs/bullmq';
 import { CryptoModule } from '../crypto/crypto.module';
+import { QueueName } from '../queue/constants';
 import { AiService } from './ai.service';
 import { AiSettingsService } from './ai-settings.service';
 import { AiSettingsController } from './ai-settings.controller';
@@ -12,7 +14,10 @@ import { AiSettingsController } from './ai-settings.controller';
  * (CaslModule, global) are resolved without explicit imports.
  */
 @Module({
-  imports: [CryptoModule],
+  imports: [
+    CryptoModule,
+    BullModule.registerQueue({ name: QueueName.AI_QUEUE }),
+  ],
   controllers: [AiSettingsController],
   providers: [AiService, AiSettingsService],
   exports: [AiService, AiSettingsService],