Fix: auto-save grid size changes and dynamically scale grid item heights based on grid size

frontend/src/components/SettingsPage.tsx

@@ -136,6 +136,8 @@ export default function SettingsPage({ onLogout }: SettingsPageProps) {
               step="10"
               value={settings.grid_size}
               onChange={(e) => setSettings({ ...settings, grid_size: e.target.value })}
+              onMouseUp={handleSave}
+              onTouchEnd={handleSave}
               className="w-full max-w-xs accent-[var(--color-accent)]"
             />
           </div>