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/music/provider.ts

@@ -15,6 +15,13 @@ export interface SongWithUrl extends Song {
   url: string;
 }
 
+/** getSongUrl 解析结果。trialDuration 缺省 = 完整可播放（VIP 账号 / 免费曲）。 */
+export interface SongUrlResult {
+  url: string;
+  /** 试听片段时长（秒）。VIP/免费曲为 undefined → 调用方回退完整 duration。 */
+  trialDuration?: number;
+}
+
 export interface Playlist {
   id: string;
   name: string;
@@ -68,7 +75,7 @@ export interface MusicProvider {
   readonly platform: "netease" | "qq" | "bilibili" | "youtube";
 
   search(query: string, limit?: number): Promise<SearchResult>;
-  getSongUrl(songId: string, quality?: string): Promise<string | null>;
+  getSongUrl(songId: string, quality?: string): Promise<SongUrlResult | null>;
   setQuality(quality: string): void;
   getQuality(): string;
   getSongDetail(songId: string): Promise<Song | null>;