add a status-bar theme switcher with live popover (T-234)

A far-right status-bar control shows the current theme and opens an
anchored popover (not the full-screen modal) to switch live: click or
keyboard (arrow/Enter to pick, Esc/tap-away to dismiss without change).
Reuses ThemeController.available/select; the theme.pick palette command
is unchanged (D-6 parity). Registered at priority 110 so it sits in the
status bar's right group.

Closes T-234 (under no parent; demo polish).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/theme_picker/src/extension.dart

@@ -1,5 +1,6 @@
 import 'package:clide/clide.dart';
 import 'package:clide/builtin/theme_picker/src/picker_view.dart';
+import 'package:clide/builtin/theme_picker/src/theme_status_item.dart';
 import 'package:clide/extension/extension.dart';
 
 class ThemePickerExtension extends ClideExtension {
@@ -26,6 +27,14 @@ class ThemePickerExtension extends ClideExtension {
           defaultBinding: 'ctrl+k',
           run: _pick,
         ),
+        // Always-visible switcher in the far-right status bar (T-234).
+        // priority >= 100 places it in the right group; registered after
+        // ipc-status so it sits to its right.
+        StatusItemContribution(
+          id: 'theme-picker.switcher',
+          priority: 110,
+          build: (_) => const ThemeSwitcherStatusItem(),
+        ),
       ];
 
   Future<IpcResponse> _pick(List<String> args) async {