feat: integrate Milkdown editor for note-taking functionality

- Added Milkdown dependencies: @milkdown/kit, @milkdown/react, @milkdown/theme-nord.
- Implemented MilkdownEditor component for rich text editing in notes.
- Updated /notes/$noteId route to include editable title and auto-saving functionality.
- Enhanced UI with loading states, saving indicators, and delete confirmation dialog.
- Applied Milkdown-specific CSS overrides for consistent theming and styling.
- Improved note update logic with debounced saving and cleanup on unmount.

package.json

@@ -47,6 +47,9 @@
   "dependencies": {
     "@fontsource/geist": "^5.2.8",
     "@hello-pangea/dnd": "^18.0.1",
+    "@milkdown/kit": "^7.18.0",
+    "@milkdown/react": "^7.18.0",
+    "@milkdown/theme-nord": "^7.18.0",
     "@tailwindcss/vite": "^4.2.0",
     "@tanstack/react-query": "^5.90.21",
     "@tanstack/react-router": "^1.161.1",