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.

src/renderer/components/layout/AppShell.tsx

@@ -69,7 +69,7 @@ export function AppShell({ children }: AppShellProps) {
               className="text-[9px] text-muted-foreground/30 tracking-widest uppercase font-medium"
               style={{ writingMode: 'vertical-rl', transform: 'rotate(180deg)' }}
             >
-              keep scrolling up for AI
+              scrolling up for Adiuva
             </span>
           </div>
         </div>