fix: brainstorm infinite loop, ghost cursor, embedding ::vector cast, semantic search, billing stats, usage meter accordion

- Fix useBrainstormSocket: stable guestId via useRef, remove setState in cleanup
- Fix GhostCursor: direct DOM manipulation via refs, no useState re-renders
- Fix all SQL embedding queries: add ::vector cast on text columns
- Fix embedding truncation to 15000 chars (under 8192 token limit)
- Fix NoteEmbedding INSERT: remove non-existent updatedAt column
- Fix billing page: show all quota stats in grid instead of single metric
- Fix usage meter: accordion expand/collapse, per-feature detail
- Fix semantic search: rebuild 103 note embeddings, ::vector cast on vectorSearch
- Fix brainstorm expand/manual-idea/create: ::vector cast on embedding SQL

README.fr.md

@@ -2,7 +2,7 @@
 
 Une application de prise de notes intelligente et powered by IA. Comme Google Keep, mais avec des notebooks, la recherche semantique, des agents IA et un serveur MCP integre.
 
-**[Read in English](README.md)** | **[Guide complet](GUIDE.md)**
+**[Read in English](README.md)** | **[Guide complet](GUIDE.md)** | **[Guide utilisateur (captures)](docs/guide-utilisateur/README.md)**
 
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