fix: restore Expand/Minimize button in AI panel + dynamic width, note thumbnail SVG placeholder with emoji/letter

memento-note/components/note-editor.tsx

@@ -899,7 +899,7 @@ export function NoteEditor({ note, readOnly = false, onClose, fullPage = false }
 
           {/* ── Side panel: AI Chat ── */}
           {aiOpen && (
-            <div className="w-[400px] h-full self-stretch border-l border-black/10 dark:border-white/10 bg-background flex flex-col z-50 shrink-0">
+            <div className="h-full self-stretch bg-background flex flex-col z-50 shrink-0">
               <ContextualAIChat
                 onClose={() => setAiOpen(false)}
                 noteTitle={title}