feat(sync): 长语音音频本地化(voice_clip media_hash+download+local-first playback)

Mirror download_call_recordings pattern for voice_clips:
- VoiceClip.media_hash column + Alembic migration (c4d5e6f7a8b9)
- VoiceClipOut.media_hash + frontend VoiceClip.media_hash type
- download_voice_clip_audio in app/scraper/media.py (resilient, sha256-dedup,
  same download_url/upsert_media helpers as call recordings)
- sync_voice_clip_audio orchestrator wrapper (commits own SyncRun, mirrors
  sync_call_recordings semantics)
- scheduler: _run_voice_clip_audio + ENTITY_FUNCS['voice_clip_audio'] +
  appended to daily _run_all job (after voice_clips)
- VoiceClipModal playClip local-first: /api/media/{media_hash} with OSS
  oss_file_name fallback (mirrors CallList.playRecord)

Tested: 376 pytest pass; vue-tsc clean; migration applied; 1523/1533 clips
localized (10 pending are genuine upstream HTTP 404s — resilient skip).

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

yunke-server/app/db/models.py

@@ -516,6 +516,12 @@ class VoiceClip(Base):
     duration_format: Mapped[str | None] = mapped_column(String(32), nullable=True)
     channel: Mapped[str] = mapped_column(String(16), nullable=False)
 
+    # sha256 media_hash of the localized audio blob (FK -> Media.media_hash);
+    # NULL until sync_voice_clip_audio downloads it. Populated by the
+    # voice_clip_audio sync pass; playback prefers /api/media/{this} over the
+    # OSS oss_file_name URL.
+    media_hash: Mapped[str | None] = mapped_column(String(64), nullable=True)
+
     # LOCAL-only manual match: references customer.friend_id when an operator
     # has associated this clip with a specific customer (好友). NULL = unmatched.
     # The mirror never pushes this back to 云客 — it's our own bookkeeping for