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/[sessionId]/expand/route.ts

@@ -67,7 +67,7 @@ async function getParentContext(
            FROM "NoteEmbedding" e
            JOIN "Note" n ON n.id = e."noteId"
            WHERE n."userId" = $1 AND n."trashedAt" IS NULL AND n.id NOT IN (${excludeList})
-           ORDER BY e.embedding <=> $2::vector
+           ORDER BY e.embedding::vector <=> $2::vector
            LIMIT 5`,
           hostUserId, vectorStr
         ) as any[]

memento-note/app/api/brainstorm/[sessionId]/manual-idea/route.ts

@@ -131,7 +131,7 @@ export async function POST(
              FROM "NoteEmbedding" e
              JOIN "Note" n ON n.id = e."noteId"
              WHERE n.id IN (${idList}) AND n."trashedAt" IS NULL
-             ORDER BY e.embedding <=> $1::vector
+             ORDER BY e.embedding::vector <=> $1::vector
              LIMIT 3`,
             vectorStr
           ) as any[]
@@ -142,7 +142,7 @@ export async function POST(
              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 3`,
             aiUserId, vectorStr
           ) as any[]

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[]