Introduce PlayerAdapter contract; decision logic shared in Rust backend

Establish a decoupled player boundary so UI and backend interact with video
through one contract, with the HTML5 (Linux/interim-Android) and native
(ExoPlayer) providers as interchangeable primitive-executor adapters.

- PlayerAdapter interface + AdapterHost callback bag (adapters/types.ts): the
  adapter owns only decision-free element PRIMITIVES (seekElement, reloadSource,
  play/pause, setVolume, selectSubtitle); it never branches on strategy.
- Seek/audio-track DECISIONS stay in Rust (player_seek_video / _switch_audio_track
  return a strategy); the facade dispatches the chosen primitive to the active
  adapter. Both providers share the one decision path — logic lives once, in Rust.
- Facade holds the active adapter; a new ControlCommand PlayerStatusEvent lets
  backend control (lockscreen/remote/sleep) drive the webview <video> element.
- Html5PlayerAdapter resolves the LIVE element via the bridge (fixes play/pause
  silently no-opping when the element was re-bound).
- Do not emit a "stopped" player state on natural end-of-video: it flipped the
  player/mode to idle mid-handoff and suppressed next-episode auto-advance under
  a sleep timer. Jellyfin progress reporting is preserved; the backend's
  on_video_playback_ended owns the transition.
- VideoPlayer net -300 lines (strategy/HLS-reload logic relocated to the adapter).
- Adds 20 adapter unit tests; existing suites stay green (vitest 457, cargo 416).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/player/adapters/nativeAdapter.test.ts

@@ -0,0 +1,88 @@
+/**
+ * Unit tests for NativePlayerAdapter — thin delegate to backend commands.
+ * Pins the primitive→command mapping so the ExoPlayer path stays correct.
+ */
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+const playerPlay = vi.fn((..._a: any[]): any => ({}));
+const playerPause = vi.fn((..._a: any[]): any => ({}));
+const playerToggle = vi.fn((..._a: any[]): any => ({ state: "playing" }));
+const playerSetVolume = vi.fn((..._a: any[]): any => ({}));
+const playerToggleMute = vi.fn((..._a: any[]): any => ({}));
+const playerSetSubtitleTrack = vi.fn((..._a: any[]): any => ({}));
+
+vi.mock("$lib/api/bindings", () => ({
+  commands: {
+    playerPlay: (...a: any[]) => playerPlay(...a),
+    playerPause: (...a: any[]) => playerPause(...a),
+    playerToggle: (...a: any[]) => playerToggle(...a),
+    playerSetVolume: (...a: any[]) => playerSetVolume(...a),
+    playerToggleMute: (...a: any[]) => playerToggleMute(...a),
+    playerSetSubtitleTrack: (...a: any[]) => playerSetSubtitleTrack(...a),
+  },
+}));
+
+import { NativePlayerAdapter } from "./nativeAdapter";
+import type { AdapterHost } from "./types";
+
+function makeHost(): AdapterHost {
+  return {
+    onState: vi.fn(), onPosition: vi.fn(), onMediaLoaded: vi.fn(), onEnded: vi.fn(),
+    onError: vi.fn(), onStreamUrlChanged: vi.fn(), onBuffering: vi.fn(), onReady: vi.fn(),
+  };
+}
+
+describe("NativePlayerAdapter", () => {
+  let adapter: NativePlayerAdapter;
+  beforeEach(() => {
+    vi.clearAllMocks();
+    adapter = new NativePlayerAdapter(makeHost());
+  });
+
+  it("is a native-kind adapter", () => {
+    expect(adapter.kind).toBe("native");
+  });
+
+  it("delegates play/pause to backend commands", async () => {
+    await adapter.play();
+    await adapter.pause();
+    expect(playerPlay).toHaveBeenCalledTimes(1);
+    expect(playerPause).toHaveBeenCalledTimes(1);
+  });
+
+  it("toggle() reflects the backend's resulting playing state", async () => {
+    expect(await adapter.toggle()).toBe(true);
+    expect(playerToggle).toHaveBeenCalledTimes(1);
+  });
+
+  it("records position on seek/reload primitives (backend does the real work)", async () => {
+    await adapter.seekElement(55, 0);
+    expect(adapter.getPosition()).toBe(55);
+    await adapter.reloadSource("ignored", 200);
+    expect(adapter.getPosition()).toBe(200);
+  });
+
+  it("load() seeds a resume position", async () => {
+    await adapter.load("url", {
+      mediaId: "m", mediaSourceId: null, needsTranscoding: false,
+      initialPosition: 90, isLive: false, audioTrackIndex: null,
+      knownDuration: 0, subtitleTracks: [],
+    });
+    expect(adapter.getPosition()).toBe(90);
+  });
+
+  it("setVolume clamps and delegates; setMuted toggles mute", () => {
+    adapter.setVolume(2);
+    expect(playerSetVolume).toHaveBeenCalledWith(1);
+    adapter.setMuted(true);
+    expect(playerToggleMute).toHaveBeenCalledTimes(1);
+  });
+
+  it("selectSubtitle maps null to disable and uses arrayIndex when given", async () => {
+    await adapter.selectSubtitle(null);
+    expect(playerSetSubtitleTrack).toHaveBeenCalledWith(null);
+    await adapter.selectSubtitle(5, 2);
+    expect(playerSetSubtitleTrack).toHaveBeenCalledWith(2);
+  });
+});