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/manifest/route.ts

@@ -6,7 +6,7 @@ export async function GET() {
       name: "Memento Notes",
       short_name: "Memento",
       description: "A smart, local-first note taking app with AI capabilities.",
-      start_url: "/",
+      start_url: "/home",
       display: "standalone",
       background_color: "#F2F0E9",
       theme_color: "#1C1C1C",