feat: resolve trial-only playback via trialDuration/effectiveDuration

VIP songs for non-VIP accounts return a ~30s trial fragment. The player used the full duration for isNearEnd, so the trial end didn't trigger auto-advance (~60s stall), and currentSong.duration stayed full, leaving the UI progress stuck.

- provider.ts: SongUrlResult {url, trialDuration?}; getSongUrl signature
- netease.ts: parseNeteaseTrial (freeTrialInfo start/end in seconds) + getSongUrl
- qq.ts: parseQqTrial (isTryout/tryEnd) + getSongUrl
- bilibili/youtube: getSongUrl returns {url}
- instance.ts: resolveAndPlay uses effectiveDuration = trialDuration ?? duration -> nearEnd at trial end -> native auto-advance; BotStatus.effectiveDuration
- VIP account: freeTrialInfo absent -> full duration -> full playback (no toggle)

Backward compatible (optional fields; getSongUrl has a single caller, updated).
Tests: parseTrial assertions (seconds/alias/ms-fallback). 14 pass.

src/bot/instance.ts

@@ -49,6 +49,8 @@ export interface BotStatus {
   volume: number;
   playMode: PlayMode;
   elapsed: number; // ground truth elapsed seconds from frame count
+  /** 当前曲实际播放时长（秒）。试听片段=试听秒数；完整曲=duration。缺失时前端回退 currentSong.duration。 */
+  effectiveDuration?: number;
 }
 
 export class BotInstance extends EventEmitter {
@@ -78,6 +80,8 @@ export class BotInstance extends EventEmitter {
   private fmProvider: MusicProvider | null = null;
   /** Results of the most recent !search, for "#N" selection (issue #90). */
   private lastSearchResults: Song[] = [];
+  /** 当前曲实际播放时长（试听片段秒数或完整 duration）；resolveAndPlay 赋值。 */
+  private effectiveDuration: number | undefined;
 
   constructor(options: BotInstanceOptions) {
     super();
@@ -460,8 +464,8 @@ export class BotInstance extends EventEmitter {
     this.voteSkipUsers.clear();
     const provider = this.getProviderFor(song.platform);
     try {
-      const url = await provider.getSongUrl(song.id);
-      if (!url) {
+      const result = await provider.getSongUrl(song.id);
+      if (!result?.url) {
         this.logger.warn({ songId: song.id, name: song.name }, "No URL available, skipping");
         return false;
       }
@@ -477,8 +481,10 @@ export class BotInstance extends EventEmitter {
         );
         return false;
       }
-      song.url = url;
-      this.player.play(url, 0, song.duration);
+      song.url = result.url;
+      // 试听片段用试听时长（让 player nearEnd 正确触发自动切歌）；完整曲回退 song.duration
+      this.effectiveDuration = result.trialDuration ?? song.duration;
+      this.player.play(result.url, 0, this.effectiveDuration);
       // Fresh playback (re)start — clear auto-pause so a later occupancy
       // change won't try to "resume" a track the user already restarted.
       this.autoPaused = false;
@@ -1063,6 +1069,7 @@ export class BotInstance extends EventEmitter {
       volume: this.player.getVolume(),
       playMode: this.queue.getMode(),
       elapsed: this.player.getElapsed(),
+      effectiveDuration: this.effectiveDuration,
     };
   }