feat: #1798 AI数字人渲染合成管线

- 新增 AiAvatarRenderJob 数据模型 + Alembic 迁移脚本
- 新增 Schema: BRollSegment / CreateAiAvatarRenderRequest / AiAvatarRenderJobResponse
- 新增 AiAvatarRenderService: 创建/查询/列表/取消/重试渲染任务
- FFmpeg 滤镜构建: build_broll_overlay_filter (fullscreen + pip 模式)
- FFmpeg 封面提取: build_cover_extract_command
- Celery 异步任务: ai_avatar_render.execute
- 5 个 API 端点: POST 创建 / GET 列表 / GET 详情 / POST 取消 / POST 重试
- 修复 router.py 中重复注册 lipsync_router 的问题
- 44 个测试: 26 Service + 12 Route + 6 Filter
- 复用现有 drawtext/concat 滤镜，不修改现有函数签名

packages/adapters/sqlalchemy_impl/models.py

@@ -702,3 +702,34 @@ class LipsyncJobModel(Base):
     completed_at = Column(DateTime, nullable=True)
     created_at = Column(DateTime, nullable=False, default=lambda: datetime.now(timezone.utc))
     updated_at = Column(DateTime, nullable=False, default=lambda: datetime.now(timezone.utc))
+
+
+class AiAvatarRenderJob(Base):
+    """AI数字人渲染任务 — #1798"""
+
+    __tablename__ = "ai_avatar_render_jobs"
+
+    id = Column(String(36), primary_key=True)
+    user_id = Column(String(36), nullable=False, index=True)
+    project_id = Column(String(36), nullable=False, default="", index=True)
+
+    # 输入参数
+    lipsync_job_id = Column(String(36), nullable=False)
+    script_id = Column(String(36), nullable=False)
+    b_roll_segments = Column(JSON, nullable=False, default=list)
+    # b_roll_segments 格式: [{"script_segment_index": 0, "asset_url": "...", "mode": "fullscreen|pip", "start_time": 5.0, "end_time": 10.0}, ...]
+    title_config = Column(JSON, nullable=False, default=dict)
+    cover_config = Column(JSON, nullable=False, default=dict)
+
+    # 任务状态
+    status = Column(String(20), nullable=False, default="pending", index=True)
+    progress = Column(Integer, nullable=False, default=0)
+    output_video_url = Column(Text, nullable=False, default="")
+    output_cover_url = Column(Text, nullable=False, default="")
+    output_duration = Column(Float, nullable=False, default=0.0)
+    error_message = Column(Text, nullable=False, default="")
+    submitted_at = Column(DateTime, nullable=True)
+    started_at = Column(DateTime, nullable=True)
+    completed_at = Column(DateTime, nullable=True)
+    created_at = Column(DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc))
+    updated_at = Column(DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc))