refactor: update keyboard shortcuts to prevent conflicts (#100)

Change Keyboard Shortcuts dialog shortcut from Cmd+H to Cmd+.
Update memory debug shortcut from Cmd+Shift+M to Cmd+Shift+D
Modify model selector shortcut to use Cmd+Shift+M

packages/ui/src/App.tsx

@@ -157,7 +157,7 @@ function App({ apis }: AppProps) {
 
   React.useEffect(() => {
     const handleKeyDown = (e: KeyboardEvent) => {
-      if (hasModifier(e) && e.shiftKey && e.key === 'M') {
+      if (hasModifier(e) && e.shiftKey && e.key === 'D') {
         e.preventDefault();
         setShowMemoryDebug(prev => !prev);
       }