Add command palette and command registry

- Commands (with optional shortcuts and availability checks) are registered in one place;
  global shortcuts are dispatched from it, and plugins can use registerCommand later
- The quick switcher lists commands when the input starts with '>' (VS Code style),
  opened with Ctrl+Shift+P or F1 (Firefox reserves Ctrl+Shift+P), plus buttons in the
  sidebar footer and the mobile top bar; recently used commands come first
- Built-in commands: quick open, search, new note/folder, save, rename, delete, close tab,
  trash, log out
- Mount the trash dialog at the workspace level so it is not positioned inside the
  transformed mobile drawer

web/src/app/Icon.vue

@@ -14,6 +14,7 @@ const paths = {
   restore: 'M3 12a9 9 0 1 0 3-6.7L3 8M3 3v5h5',
   edit: 'M12 20h9M16.5 3.5a2.1 2.1 0 0 1 3 3L7 19l-4 1 1-4z',
   search: 'M11 18a7 7 0 1 0 0-14 7 7 0 0 0 0 14zM21 21l-4.35-4.35',
+  command: 'M18 3a3 3 0 0 0-3 3v12a3 3 0 1 0 3-3H6a3 3 0 1 0 3 3V6a3 3 0 1 0-3 3h12a3 3 0 0 0 0-6z',
 }
 defineProps<{ name: keyof typeof paths; size?: number }>()
 </script>