fix(viral-video): #2106 P0 渲染阻塞修复 + Seedance 2.5 对接 + image_analysis 持久化

P0-1: Seedance 2.5 视频生成对接
- packages/shared/ai_client.py: DoubaoClient 新增 video_generation(prompt, image_url, duration, ratio, ...)
  方法：走方舟 /contents/generations/tasks 异步任务（submit→poll→download），返回本地 MP4 路径
- packages/shared/ai_service.py: 新增 call_video_generation() 高层封装
- packages/config/base.py: 新增 doubao_video_model/doubao_video_timeout/doubao_video_poll_interval 配置
- apps/worker/.../viral_video.py _step_render 重写：按 storyboard 分镜逐段调 Seedance 生成短视频
  → ffmpeg concat 拼接 → 混入 TTS 音频（-map 0:v/1:a -shortest -c:v copy）
- 单分镜失败自动用 ffmpeg color 源占位片段兜底，保证 concat 不中断
- 新增 _normalize_storyboard/_fallback_storyboard/_build_segment_prompt/_probe_ok/_make_placeholder_clip
  等辅助函数

P0-2: _step_video_analysis import 路径修复
- from worker_app.tasks.viral_video_analyzer → from viral_video.video_analyzer import analyze_video_style
  （文件在 apps/worker/viral_video/video_analyzer.py，worker PYTHONPATH 包含 apps/worker）
- ImportError 仍兜底返回占位 style_guide，不阻塞流水线

P0-3: image_analysis 持久化
- packages/domain/viral_video.py: ViralVideoJob 新增 image_analysis: dict|None 字段
- packages/adapters/sqlalchemy_impl/models.py: viral_video_jobs 加 image_analysis JSON 列
- packages/adapters/sqlalchemy_impl/viral_video_repository.py: _to_domain/save/update 同步该字段
- alembic/versions/087_viral_video_image_analysis.py: migration 087
- run_viral_video_pipeline: step1 后立即 job.image_analysis = image_analysis 并 _save_job
- resume_viral_video_pipeline: 从 job.image_analysis 读取，不再硬编码空 dict

P1 顺手修复：
- _step_tts: 返回值统一为 Path|None，Path 不存在/ImportError/synthesize 失败均返回 None
- _step_bgm_select: BGM 素材未就绪前统一返回 None，渲染时跳过 BGM 混音
- _step_musetalk: GPU 端点未就绪前（即使有 persona_id）也直接跳过，不发 HTTP 请求
- TTS 工厂 import 路径修正: worker_app.services.tts_service_factory → services.tts_service_factory
- credits_cost 赋值保留 TODO（等 credits.deduct() 总开关）
- tests/unit/test_viral_video.py: BGM/TTS mock 对齐新返回语义
- tests/unit/test_viral_video_p0.py: 新增 15 个单测覆盖 video_analysis/storyboard 规范化/
  TTS Path 处理/BGM None/MuseTalk 跳过/call_video_generation 委托/placeholder clip/resume 读 job

packages/adapters/sqlalchemy_impl/models.py

@@ -946,6 +946,7 @@ class ViralVideoJobModel(Base):
     # 结果与状态
     status = Column(String(30), nullable=False, default="pending", index=True)
     intent_result = Column(JSON, nullable=True)
+    image_analysis = Column(JSON, nullable=True)
     result_video_url = Column(String(1000), nullable=False, default="")
     credits_cost = Column(Integer, nullable=False, default=0)
     error_msg = Column(Text, nullable=False, default="")

packages/adapters/sqlalchemy_impl/viral_video_repository.py

@@ -34,6 +34,7 @@ def _to_domain(model: ViralVideoJobModel) -> ViralVideoJob:
         style_template_id=getattr(model, "style_template_id", "") or "",
         status=ViralVideoStatus(model.status) if model.status else ViralVideoStatus.PENDING,
         intent_result=dict(model.intent_result) if model.intent_result else None,
+        image_analysis=dict(model.image_analysis) if getattr(model, "image_analysis", None) else None,
         result_video_url=model.result_video_url or "",
         credits_cost=model.credits_cost or 0,
         error_msg=model.error_msg or "",
@@ -72,6 +73,7 @@ class SQLAlchemyViralVideoJobRepository:
             style_template_id=job.style_template_id,
             status=job.status,
             intent_result=job.intent_result,
+            image_analysis=job.image_analysis,
             result_video_url=job.result_video_url,
             credits_cost=job.credits_cost,
             error_msg=job.error_msg,
@@ -91,6 +93,7 @@ class SQLAlchemyViralVideoJobRepository:
             raise ValueError(f"ViralVideoJob {job.id} not found")
         model.status = job.status
         model.intent_result = job.intent_result
+        model.image_analysis = job.image_analysis
         model.result_video_url = job.result_video_url
         model.credits_cost = job.credits_cost
         model.error_msg = job.error_msg