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)

AGENTS.md

@@ -1,12 +1,29 @@
 # AGENTS.md
 
-> **Monorepo note:** `web/` is a separate Next.js landing page with its own `AGENTS.md`. This file covers the Flutter app only.
+---
 
-## Workflow
+# Author Preferences
 
-- In plan mode, interview thoroughly — ask about UI/UX, tradeoffs, and edge cases before coding
-- When new code supersedes existing functionality, find and remove everything it makes redundant
-- Favor parallel tool calls and subagents when tasks are independent
+## Code Opinions
+
+- Package imports (`import 'package:frosty/...'`), not relative imports
+- Trailing commas always
+- Single quotes
+- Extract related/grouped logic (state, reactions, actions) into dedicated stores when it improves readability — keep widgets focused on rendering
+
+## Infrastructure Checklist
+
+When creating new infrastructure (screens, API clients, stores), use exploration findings as a **checklist** — systematically verify each convention is followed before writing code.
+
+## Never
+
+- Never edit `.g.dart` files directly — always regenerate with `dart run build_runner build`
+
+---
+
+# Project
+
+Flutter mobile app for browsing Twitch on iOS and Android. Uses MobX for state management with code generation.
 
 ## Commands
 
@@ -29,7 +46,7 @@ dart run build_runner build --delete-conflicting-outputs             # Same, but
 - `lib/widgets/` — Shared widgets
 - `lib/utils/` — Utility functions
 
-## Architecture (non-obvious bits)
+## Architecture
 
 - Feature stores live in `lib/screens/{feature}/stores/` — don't create new top-level store files (only `lib/stores/` holds global stores)
 - All API services extend `BaseApiClient` (`lib/apis/base_api_client.dart`) — don't create standalone API classes
@@ -39,9 +56,6 @@ dart run build_runner build --delete-conflicting-outputs             # Same, but
 
 - After changing MobX stores or `@JsonSerializable` models, regenerate with `dart run build_runner build`. Never edit `.g.dart` files directly. Commit `.g.dart` files to source control.
 - The secure storage cleanup in `main.dart` looks unnecessary but handles an Android/iOS edge case where secure storage persists after uninstall. Don't remove it.
-- Use package imports (`import 'package:frosty/...'`), not relative imports
-- Always include trailing commas
-- Use single quotes
 
 ## Testing
 
@@ -49,9 +63,3 @@ dart run build_runner build --delete-conflicting-outputs             # Same, but
 - HTTP mocking: `http_mock_adapter` (`DioAdapter`) — use full URLs in `onGet`/`onPost`
 - General mocking: `mocktail` (no codegen required)
 - Fixtures live in `test/fixtures/` (e.g., `irc_messages.dart`, `api_responses.dart`)
-
-## Commits
-
-Conventional commits: `type(scope): description` — lowercase, no trailing period, tightly scoped (e.g., `fix(chat): correct landscape bottom padding in bottom bar`). Append `!` before the `:` for breaking changes (e.g., `feat(api)!: drop legacy auth flow`).
-
-Common types: `feat`, `fix`, `chore`, `refactor`, `docs`, `test`, `perf`, `style`. Scope is the affected area (e.g., `chat`, `video`, `api`).