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/components/brainstorm/brainstorm-page.tsx

@@ -213,7 +213,7 @@ export function BrainstormPage() {
         setConvertToast({ noteTitle: result.title || idea.title, noteId: result.id })
         setTimeout(() => {
           setConvertToast(null)
-          router.push(`/?openNote=${result.id}`)
+          router.push(`/home?openNote=${result.id}`)
         }, 2000)
       }
     } catch {}
@@ -228,7 +228,7 @@ export function BrainstormPage() {
         setExportToast({ noteTitle: result.title || t('brainstorm.exportDefaultNoteTitle'), notebookName })
         setTimeout(() => {
           setExportToast(null)
-          router.push(`/?openNote=${result.id}`)
+          router.push(`/home?openNote=${result.id}`)
         }, 2000)
         return
       }
@@ -634,7 +634,7 @@ export function BrainstormPage() {
                             </div>
                             {ref.noteId && (
                               <button
-                                onClick={() => router.push(`/?openNote=${ref.noteId}`)}
+                                onClick={() => router.push(`/home?openNote=${ref.noteId}`)}
                                 className="shrink-0 px-2 py-1 text-[9px] font-bold uppercase tracking-wider rounded-lg bg-foreground/5 hover:bg-foreground/10 text-muted-foreground hover:text-foreground transition-all"
                               >
                                 {t('brainstorm.viewNote') || 'View'}