feat(quick-261022-k9k): Esc, slash and help shortcuts, settings, account and modal save keys

- '?' help dialog (ShortcutHelpDialog) listing the current screen's shortcuts
- Esc = Cancel on record forms; '/' focuses the list search
- settings forms: Save and close (Ctrl/Cmd+Enter, then /settings) and Ctrl/Cmd+S
- My account: Ctrl/Cmd+S
- modal forms: Ctrl/Cmd+S and Ctrl/Cmd+Enter submit the innermost dialog only
- docs: Keyboard shortcuts section in the admin SPA page

admin/src/components/shell/AppShell.vue

@@ -7,6 +7,7 @@ import SettingsPanel from './SettingsPanel.vue'
 import Breadcrumbs from './Breadcrumbs.vue'
 import UserMenu from './UserMenu.vue'
 import Toast from '../ui/Toast.vue'
+import ShortcutHelpDialog from './ShortcutHelpDialog.vue'
 import { ExternalLink } from '@lucide/vue'
 import { controllerIdFromPath } from '../../app/controllerRoutes'
 import { activeEntry } from '../../state/useNavigation'
@@ -92,5 +93,6 @@ const shellOffset = computed(() =>
       </main>
     </div>
     <Toast />
+    <ShortcutHelpDialog />
   </div>
 </template>