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/rich-text-editor.tsx

@@ -150,7 +150,22 @@ async function aiReformulate(text: string, option: string, language?: string): P
   })
   const data = await res.json()
   if (!res.ok) {
-    const serverMsg = typeof data?.error === 'string' && data.error.trim() ? data.error.trim() : AI_REFORMULATE_FALLBACK
+    if (data?.errorKey === 'ai.wordCountMin') {
+      throw new Error(t('ai.wordCountMin') || `Minimum ${data?.params?.min || 10} mots requis (${data?.params?.current || 0} actuels)`)
+    }
+    if (data?.errorKey === 'ai.wordCountMax') {
+      throw new Error(t('ai.wordCountMax') || `Maximum ${data?.params?.max || 500} mots (${data?.params?.current || 0} actuels)`)
+    }
+    if (data?.errorKey === 'ai.featureLocked') {
+      throw new Error(t('ai.featureLocked') || 'Cette fonctionnalité nécessite le plan PRO.')
+    }
+    if (data?.errorKey === 'ai.quotaExceeded') {
+      throw new Error(t('ai.quotaExceeded') || 'Limite mensuelle atteinte.')
+    }
+    if (data?.quotaExceeded) {
+      throw new Error(t('ai.quotaExceeded') || 'Limite mensuelle atteinte.')
+    }
+    const serverMsg = typeof data?.error === 'string' && !data.error.includes(':') ? data.error.trim() : AI_REFORMULATE_FALLBACK
     throw new Error(serverMsg)
   }
   return data.reformulatedText || data.text || text
@@ -385,6 +400,7 @@ function BubbleToolbar({ editor }: { editor: Editor | null }) {
     try {
       const lang = option === 'translate' ? (targetLang || language) : language
       const result = await aiReformulate(text, option, lang)
+      window.dispatchEvent(new Event('ai-usage-changed'))
       if (option === 'explain') {
         setAiModal({ type: 'explain', origText: text, html: result, from, to })
       } else {