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/client/src/features/workspace/services/ai-settings-service.ts

@@ -60,3 +60,8 @@ export async function testAiConnection(): Promise<IAiTestResult> {
   const req = await api.post<IAiTestResult>("/workspace/ai-settings/test");
   return req.data;
 }
+
+export async function reindexAiEmbeddings(): Promise<IAiSettings> {
+  const req = await api.post<IAiSettings>("/workspace/ai-settings/reindex");
+  return req.data;
+}