One app menu style for every picker; links go Through me by default

- AppSelect / AppMenuButton (widgets/app_menu.dart): glass menu anchored
  to its button, check on the current item, keyboard and Esc; replaces
  the Material dropdowns in Settings, player settings, Jellyfin and the
  member menu. Material menus elsewhere get the same surface by theme.
- Link page: Through me is the main choice (you can't know which sites
  need cookies); Everyone / Server fetches it sit under "Other ways".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/test/home_test.dart

@@ -87,7 +87,7 @@ void main() {
     expect(c.source, MediaKind.jellyfin);
     c.pasteText(' https://example.com/a.mkv ');
     expect(c.source, MediaKind.link);
-    expect(c.selection, const LinkMedia('https://example.com/a.mkv'));
+    expect(c.selection, const LinkMedia('https://example.com/a.mkv', relay: LinkRelay.me));
     c.pasteText('/home/me/b.mkv');
     expect(c.source, MediaKind.file);
     expect(c.selection, const FileMedia('/home/me/b.mkv'));

apps/desktop/test/jellyfin_accounts_test.dart

@@ -307,7 +307,7 @@ void main() {
       final c = MediaPickerController();
       expect(c.selection, isNull);
       c.pasteText('https://example.com/a.mkv');
-      expect(c.selection, const LinkMedia('https://example.com/a.mkv'));
+      expect(c.selection, const LinkMedia('https://example.com/a.mkv', relay: LinkRelay.me));
       c.pasteText('/home/me/b.mkv');
       expect(c.selection, const FileMedia('/home/me/b.mkv'));
       c.source = MediaKind.jellyfin;

apps/desktop/test/library_tab_test.dart

@@ -281,9 +281,18 @@ void main() {
     expect(find.descendant(of: find.byKey(const ValueKey('link-preview')), matching: find.text('A video')),
         findsOneWidget);
     expect(find.text('youtube.com · Chan'), findsOneWidget);
+    // Through me by default; the other two behind "Other ways".
+    expect(h.controller.linkRelay, LinkRelay.me);
+    expect(find.byKey(const ValueKey('link-mode-direct')), findsNothing);
+    await tester.tap(find.byKey(const ValueKey('link-other-ways')));
+    await settle(tester);
+    await tester.tap(find.byKey(const ValueKey('link-mode-server')));
+    await settle(tester);
+    expect(h.controller.linkRelay, LinkRelay.server);
     await tester.tap(find.byKey(const ValueKey('link-mode-me')));
     await settle(tester);
     expect(h.controller.linkRelay, LinkRelay.me);
+    expect(find.byKey(const ValueKey('link-mode-direct')), findsOneWidget, reason: 'stays open until closed');
     expect(find.text(linkRelayHelp(LinkRelay.me)), findsOneWidget);
     await tester.tap(find.byKey(const ValueKey('link-put-up')));
     await settle(tester, 10);

apps/desktop/test/uosc_controls_test.dart

@@ -16,6 +16,7 @@ import 'package:watch_together/src/shaders/shader_presets.dart';
 import 'package:watch_together/src/shell/settings_tab.dart';
 import 'package:watch_together/src/state/settings.dart';
 import 'package:watch_together/src/update/update_controller.dart';
+import 'package:watch_together/src/widgets/app_menu.dart';
 
 // The experimental mpv-style (uosc) controls, piece by piece (never the
 // session screen or a media_kit `Video`).
@@ -466,12 +467,12 @@ void main() {
     ));
     final design = find.byKey(const ValueKey('player-design'));
     expect(find.text('Player design'), findsOneWidget);
-    expect(tester.widget<DropdownButton<bool>>(design).value, isFalse);
+    expect(tester.widget<AppSelect<bool>>(design).value, isFalse);
     await tester.tap(design);
     await tester.pumpAndSettle();
     await tester.tap(find.text('uosc').last);
     await tester.pumpAndSettle();
     expect(s.mpvControls.value, isTrue);
-    expect(tester.widget<DropdownButton<bool>>(design).value, isTrue);
+    expect(tester.widget<AppSelect<bool>>(design).value, isTrue);
   });
 }