feat(mdblist): sync watched history, scrobbles and ratings with MDBList

Connects MDBList through its OAuth device-code grant, registered as a
Device Code app so no client secret or redirect URI ships in the binary
and TV, mobile and desktop all use the same flow.

MDBList omits `verification_uri_complete`, but its device page seeds the
code field from a `user_code` query parameter and the sign-in redirect
preserves the query string, so the activation link is built locally and
the dialog's open button lands on a filled-in form instead of an empty
one. A server-supplied complete URL still wins if one ever appears.

Poll state is read from the response body rather than the status code:
`authorization_pending` and `slow_down` both arrive as HTTP 400, and a
missing grant answers 404 `device_not_found`.

Writes go out as real-time `/scrobble/*` reports plus `/sync/watched`
for the marks that never pass through the player, with ratings on
`/sync/ratings`. Matching uses IMDb and TMDb only — MDBList's id block
has no `tvdb` field, so a TVDB-only item is skipped rather than written
under an empty id block.

lib/screens/settings/tracker_service_info.dart

@@ -6,6 +6,7 @@ import '../../models/catalog/catalog_item.dart';
 import '../../providers/trackers_provider.dart';
 import '../../services/trackers/anilist/anilist_tracker.dart';
 import '../../services/trackers/mal/mal_tracker.dart';
+import '../../services/trackers/mdblist/mdblist_tracker.dart';
 import '../../services/trackers/simkl/simkl_tracker.dart';
 import '../../services/trackers/tracker.dart';
 import '../../services/trackers/tracker_constants.dart';
@@ -88,5 +89,11 @@ class TrackerServiceInfo {
       ratingSource: SimklTracker.instance,
       startConnection: startSimklConnection,
     ),
+    TrackerServiceInfo.shared(
+      TrackerConfig.mdblist(),
+      logoSource: CatalogSourceId.mdblist,
+      ratingSource: MdblistTracker.instance,
+      startConnection: startMdblistConnection,
+    ),
   ];
 }

lib/screens/settings/tracker_settings_screen.dart

@@ -7,6 +7,7 @@ import '../../models/trackers/device_code.dart';
 import '../../providers/trackers_provider.dart';
 import '../../services/trackers/anilist/anilist_tracker.dart';
 import '../../services/trackers/mal/mal_tracker.dart';
+import '../../services/trackers/mdblist/mdblist_tracker.dart';
 import '../../services/trackers/oauth_proxy_client.dart';
 import '../../services/trackers/simkl/simkl_tracker.dart';
 import '../../services/trackers/tracker_constants.dart';
@@ -60,6 +61,20 @@ Future<void> startSimklConnection(BuildContext context) {
   );
 }
 
+Future<void> startMdblistConnection(BuildContext context) {
+  final account = context.read<TrackersProvider>();
+  final name = t.services.names.mdblist;
+  return launchTrackerConnect<DeviceCode>(
+    context,
+    isBusyOrConnected: account.isConnecting(TrackerService.mdblist) || account.isMdblistConnected,
+    serviceName: name,
+    connect: (cb) => account.connectMdblist(onCodeReady: cb),
+    onCancel: account.cancelConnect,
+    buildDialog: (p, cancel) => DeviceCodeDialog(code: p, serviceName: name, onCancel: cancel),
+    urlFor: (p) => p.verificationUrlComplete ?? p.verificationUrl,
+  );
+}
+
 /// Per-service wiring for [TrackerSettingsScreen]. Keeps tracker-specific
 /// method names out of the shared screen body.
 class TrackerConfig {
@@ -107,11 +122,20 @@ class TrackerConfig {
     onScrobbleChanged: SimklTracker.instance.setEnabled,
     disconnect: (a) => a.disconnectSimkl(),
   );
+
+  static TrackerConfig mdblist() => TrackerConfig(
+    service: TrackerService.mdblist,
+    displayName: t.services.names.mdblist,
+    isConnected: (a) => a.isMdblistConnected,
+    username: (a) => a.mdblistUsername,
+    onScrobbleChanged: MdblistTracker.instance.setEnabled,
+    disconnect: (a) => a.disconnectMdblist(),
+  );
 }
 
-/// Shared settings screen for MAL, AniList, and Simkl. Only reachable while
-/// connected — if the session drops (refresh failure, back-nav race) we pop
-/// back to the hub.
+/// Shared settings screen for MAL, AniList, Simkl and MDBList. Only reachable
+/// while connected — if the session drops (refresh failure, back-nav race) we
+/// pop back to the hub.
 class TrackerSettingsScreen extends StatelessWidget {
   final TrackerConfig config;
   const TrackerSettingsScreen({super.key, required this.config});