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

memento-note/app/api/brainstorm/route.ts

@@ -44,7 +44,7 @@ async function autoContextSearch(
          FROM "NoteEmbedding" e
          JOIN "Note" n ON n.id = e."noteId"
          WHERE n."userId" = $1 AND n."trashedAt" IS NULL
-          ORDER BY e.embedding <=> $2::vector
+          ORDER BY e.embedding::vector <=> $2::vector
          LIMIT 8`,
         userId, vectorStr
       ) as any[]