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/components/layout/Header.tsx

@@ -425,7 +425,7 @@ export const Header: React.FC = () => {
             </button>
           </TooltipTrigger>
           <TooltipContent>
-            <p>Keyboard Shortcuts ({getModifierLabel()}+H)</p>
+            <p>Keyboard Shortcuts ({getModifierLabel()}+.)</p>
           </TooltipContent>
         </Tooltip>
       </div>