feat(ux): epic UX design improvements across agents, chat, notes, and i18n

Comprehensive UI/UX updates including agent card redesign, chat container
improvements, note editor enhancements, memory echo notifications, and
updated translations for all 15 locales.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

keep-notes/lib/types.ts

@@ -75,6 +75,7 @@ export interface Note {
   notebookId?: string | null;
   notebook?: Notebook | null;
   autoGenerated?: boolean | null;
+  aiProvider?: string | null;
   // Search result metadata (optional)
   matchType?: 'exact' | 'related' | null;
   searchScore?: number | null;