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/contextual-ai-chat.tsx

@@ -564,16 +564,16 @@ export function ContextualAIChat({
 
         <div className="p-6 border-b border-border/60 space-y-1.5 bg-white/50 dark:bg-black/20 backdrop-blur-md shrink-0">
           <div className="flex items-center justify-between">
-            <div>
+            <div className="min-w-0 flex-1">
               <h3 className="flex items-center gap-2 font-serif text-xl font-medium text-ink">
-                <Sparkles size={18} className="text-brand-accent" />
+                <Sparkles size={18} className="text-brand-accent shrink-0" />
                 {t('ai.assistantTitle') || 'IA Assistant'}
               </h3>
               <p className="text-[11px] text-concrete uppercase tracking-wider font-medium opacity-60 truncate">
                 "{noteTitle || t('ai.currentNote')}"
               </p>
             </div>
-            <div className="flex items-center gap-1 shrink-0">
+            <div className="flex items-center gap-1 shrink-0 ml-2">
               <button
                 onClick={() => setExpanded(e => !e)}
                 className="p-1.5 hover:bg-slate-100 dark:hover:bg-white/10 rounded-lg transition-colors text-concrete"
@@ -584,6 +584,7 @@ export function ContextualAIChat({
               <button
                 onClick={onClose}
                 className="p-1.5 hover:bg-slate-100 dark:hover:bg-white/10 rounded-lg transition-colors text-concrete"
+                title={t('general.close') || 'Fermer'}
               >
                 <X size={18} />
               </button>