fix(ai): show live reindex progress in semantic-search settings

The "Indexed X of Y pages" counter stayed stuck at "478 of 478" during a
manual "Reindex now" run instead of resetting to 0 and climbing. The status
reports indexedPages = countIndexedPages (DISTINCT pages with >=1 embedding
row), but reindex hard-replaces each page in its OWN small transaction, so
nearly all pages always have rows -> the count never drops.

Add a per-workspace live reindex-progress record in Redis (reusing the
existing global ioredis client via RedisService, no new Redis config):
- EmbeddingReindexProgressService: start/increment/clear/get over a Redis hash
  with a 1h TTL self-clean; all best-effort/cosmetic so a Redis failure degrades
  to the existing DB-count behavior.
- AiSettingsService.reindex seeds {total, done:0, startedAt} at enqueue time so
  the very first poll already reports done=0.
- EmbeddingIndexerService.reindexWorkspace overwrites total with the real page
  count at start, increments done per processed page (success or handled
  failure), and clears the record in a finally (covers success, fatal abort,
  and the unconfigured early-return) so a failed run never sticks.
- AiSettingsService.getMasked returns the live run numbers when a progress
  record is active (plus an optional reindexing flag), else falls back to
  countIndexedPages/countEmbeddablePages.

Per-page edits (reindexPage) never touch the workspace progress record, and no
mass up-front delete is introduced (search availability preserved).

Tests: indexer sets/increments/clears progress (incl. fatal abort and
unconfigured early-return); status reports run progress when active and falls
back when not.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -48,6 +48,9 @@ export interface IAiSettings {
   // RAG indexing coverage (pages indexed for semantic search).
   indexedPages: number;
   totalPages: number;
+  // True while a full workspace reindex is actively running; the counts above
+  // then reflect the live run progress (done climbs 0 -> total).
+  reindexing?: boolean;
 }
 
 // Update payload. Key semantics (same for `apiKey` and `embeddingApiKey`):