feat(video,chat): native player, ad-break awareness, chat send/delay reliability, and tab redesign (#567)

Squash-merge commit. Covers four areas: native video player, chat reliability, multi-tab, and hardening.

## Native video player
- Direct HLS playback via `better_native_video_player` (forked from `plug-and-pay/flutter-native-video-player`, patched on `frosty-patches` branch)
- Twitch GQL playback token fetching with platform cookie extraction (iOS Swift + Android Kotlin plugins) for authenticated streams
- Quality selection (source, 720p, 480p, 360p, 160p, audio-only) persisted per channel
- Picture-in-picture: iOS automatic inline PiP, Android auto-PiP on API 31+ guarded against older devices
- Latency polling, chat latency sync, stall detection/recovery, startup auto-pause recovery, watchdog timers
- **Twitch stitched-ad break detection** (HLS `EXT-X-DATERANGE`) on both platforms, emitting `adBreakChanged` so the host suspends latency/stall recovery and chat sync during ads (program-date-time is unreliable then). Matches `CLASS="twitch-stitched-ad"` / `ID="stitched-ad-"` **and** the `X-TV-TWITCH-AD-*` attribute prefix (the durable signal streamlink/yt-dlp use)
- Shared `VideoPlayerInterface` so WebView and native paths are interchangeable via settings toggle
- `PlaybackAccessToken` model, `TwitchGqlApi` client

## Chat delay & send reliability
- **Optimistic send-finalize**: Twitch acks a sent message with a per-PRIVMSG USERSTATE (not an echo), which it can intermittently drop — more so under a long chat delay. A missing ack no longer shows a false "message may not have been sent" error; the send is finalized optimistically (local echo rendered), and only genuine rejection NOTICEs surface an error. Ack timeout scaled by the chat delay.
- **Per-line chat-delay bypass**: control/state lines (USERSTATE/ROOMSTATE/GLOBALUSERSTATE), rejection NOTICEs, the reconnect notice, and untagged server lines bypass the delay so send-acks and PONGs aren't stalled; only displayable chat content is delayed, staying in sync with delayed video.
- **Measured chat bottom-bar height**: the message list reflows to the composer's real measured height, fixing the input overlapping messages when a long message expands it (replaces a fixed-constant estimate).
- IRC tag parsing handles valueless and escaped tags per the IRCv3 message-tags spec (fixes a recent-messages RangeError on certain tags).

## Chat / multi-tab
- Redesigned tab chips: unread dot indicator, chips dim until WebSocket connects
- Animated tab options popover replacing `MenuAnchor` (no animation hook in Flutter 3.44)
- Simplified `ChatTabs` from `StatefulWidget` to `StatelessWidget`
- Focus-current-channel fade bump to 0.55; section-header alpha lifted to match the muted-label tier
- `addTab` now calls `setActiveTab` to snapshot outgoing tab's `lastSeenMessageId` — fixes spurious unread dots after adding a tab
- `onActivateSourceTab` threaded into `ChatUserModal` so Reply in merged mode switches to the correct source tab's composer

## Bug fixes and hardening
- **Reverted the experimental iOS low-latency mode** (5s live-edge join + 1.05x catch-up): AVPlayer can't sustain <~18s on Twitch (declared `TARGETDURATION:6` paces playlist refreshes), and the offset starved the buffer into pause-on-launch. Default join distance restored.
- Fork (Android): **cap `BEHIND_LIVE_WINDOW` recovery** so a stream repeatedly falling off the live window can't silently re-prepare forever; emits `error` on exhaustion so the host recovery ladder takes over
- Guard all Android `setAutoPipMode` calls with `_autoPipAvailable` — prevents `PlatformException` on Android 8–11; check `_disposed` after `isAutoPipAvailable` await to prevent post-dispose auto-PiP re-enable
- Remove `_isInPipMode` guard from `_onPaused` so `_paused` tracks actual state, fixing PiP play/pause toggle getting stuck
- Tighten iOS cookie domain check to exact `twitch.tv` / `.twitch.tv` suffix
- Invalidate the stored web session token when Twitch rejects it with a 401 (profile card flips back to unlinked; future loads skip the doomed authenticated request), and re-extract the cookie on launch when logged in without a linked session
- Send `play_session_id` and `player_backend=mediaplayer` to Usher, matching the web client / streamlink
- Fork (iOS): restore program-date-time latency measurement (a prior rev measured distance to the manifest edge, reading ~0s and silently disabling high-latency recovery / chat-delay auto-sync); release platform views on dispose (per-stream view + AVPlayerViewController leak), track the observed AVPlayerItem for KVO removal (sibling-view crash), main-thread seek results, resolve superseded load futures
- Fork (Android): clean up method handlers orphaned by PiP-time view disposal (leaked audio-focus listeners), drop the live-offset re-anchoring seekTo on metadata updates (latency creep), restore pre-duck volume, respect user pause in the stall watchdog, resolve superseded load futures
- Deep review pass: expire the quality-switch flag so stall recovery isn't disabled for the session, cap latency-driven recovery (clock-skew loop), generation-guard the error overlay, two-strike offline confirmation, controller null-safety on quality switch
- Tighten `/me` local-echo match (no longer renders `/meow ...` as an action); clear pending send text on disconnect

## Web / docs
- Remove stale Cloudflare Images binding from `wrangler.jsonc` (covered by `images.unoptimized: true`)
- Correct `web/AGENTS.md` Cache Components claim (feature not enabled)
- Repo and agent config cleanup

## Test plan
- [x] `flutter analyze` — clean (frosty + plugin lib)
- [x] `flutter test` — 319/319 pass (adds `ChatLatencySync`, `StreamInfoPoller`, video timing invariants, `PlaybackAccessToken`, IRC tag parsing)
- [x] Android plugin Kotlin compiles against the bumped fork rev
- [ ] Native player plays live streams on iOS and Android
- [ ] Quality switching works and persists across channel reopens
- [ ] PiP enters/exits correctly; pause/resume toggle in PiP window works
- [ ] Audio-only mode does not crash on Android < API 31
- [ ] Sending under a long synced chat delay no longer shows a false "may not have been sent" error
- [ ] Long composer text reflows the message list (no input/message overlap)
- [ ] Multi-tab: adding a tab does not mark previous tab as unread
- [ ] Merged chat: Reply from user modal targets the correct tab's composer

🤖 Generated with [Claude Code](https://claude.com/claude-code)

lib/screens/settings/stores/auth_store.dart

@@ -9,6 +9,7 @@ import 'package:frosty/apis/twitch_api.dart';
 import 'package:frosty/constants.dart';
 import 'package:frosty/main.dart';
 import 'package:frosty/screens/settings/stores/user_store.dart';
+import 'package:frosty/services/cookie_extractor.dart';
 import 'package:frosty/widgets/frosty_dialog.dart';
 import 'package:mobx/mobx.dart';
 import 'package:webview_flutter/webview_flutter.dart';
@@ -27,6 +28,9 @@ abstract class AuthBase with Store {
   /// The shared_preferences key for the user token.
   static const _userTokenKey = 'user_token';
 
+  /// The secure storage key for the GQL web cookie token.
+  static const _gqlTokenKey = 'gql_token';
+
   /// The Twitch API service for making requests.
   final TwitchApi twitchApi;
 
@@ -49,6 +53,10 @@ abstract class AuthBase with Store {
   @readonly
   String? _token;
 
+  /// Web cookie token extracted from the login WebView for GQL ad-free playback.
+  @readonly
+  String? _gqlToken;
+
   /// Whether the user is logged in or not.
   @readonly
   var _isLoggedIn = false;
@@ -83,6 +91,7 @@ abstract class AuthBase with Store {
     // When redirected to the redirect_uri, there will be another redirect to "https://www.twitch.tv/?no-reload=true".
     // Checking for this will ensure that the user has automatically logged in to Twitch on the WebView itself.
     if (request.url == 'https://www.twitch.tv/?no-reload=true') {
+      _extractGqlToken();
       if (routeAfter != null) {
         navigatorKey.currentState?.pop();
         navigatorKey.currentState?.push(
@@ -211,12 +220,36 @@ abstract class AuthBase with Store {
 
   AuthBase({required this.twitchApi}) : user = UserStore(twitchApi: twitchApi);
 
+  Future<void> _extractGqlToken() async {
+    try {
+      final token = await CookieExtractor.extractTwitchAuthToken();
+      if (token != null) {
+        runInAction(() {
+          _gqlToken = token;
+        });
+        await _storage.write(key: _gqlTokenKey, value: token);
+      }
+    } catch (e) {
+      debugPrint('GQL token extraction failed: $e');
+    }
+  }
+
+  /// Clears the stored web session token after Twitch rejects it, so the
+  /// profile card reflects the unlinked state and future stream loads skip
+  /// the doomed authenticated request.
+  @action
+  Future<void> invalidateGqlToken() async {
+    _gqlToken = null;
+    await _storage.delete(key: _gqlTokenKey);
+  }
+
   /// Initialize by retrieving a token if it does not already exist.
   @action
   Future<void> init() async {
     try {
       // Read and set the currently stored user token, if any.
       _token = await _storage.read(key: _userTokenKey);
+      _gqlToken = await _storage.read(key: _gqlTokenKey);
 
       // If the token does not exist, get the default token.
       // Otherwise, log in.
@@ -248,6 +281,10 @@ abstract class AuthBase with Store {
         if (user.details != null) {
           _isLoggedIn = true;
           _stopReconnectLoop();
+
+          // Recover a missed web session link — the WebView cookie store may
+          // still hold a valid auth-token from a previous login.
+          if (_gqlToken == null) _extractGqlToken();
         }
       }
 
@@ -293,9 +330,11 @@ abstract class AuthBase with Store {
   Future<void> logout() async {
     try {
       _stopReconnectLoop();
-      // Delete the existing user token.
+      // Delete the existing user token and GQL token.
       await _storage.delete(key: _userTokenKey);
+      await _storage.delete(key: _gqlTokenKey);
       _token = null;
+      _gqlToken = null;
 
       // Clear the user info.
       user.dispose();