fix: 渲染管线 bool 类型配置防护 — 全面修复 'bool' object has no attribute 'get' 崩溃

根因: plan.config 中某 key 的值可能为 bool 而非 dict，
当 .get() 或 from_dict() 被调用时崩溃。
'or {}' 只能防 None/空值，防不了 True/False。

修复策略（双层防护）:
1. 治本: 所有 from_dict 方法入口加 isinstance(data, dict) 检查
   - chroma_key_config.py / color_grade_config.py / noise_reduction_config.py
   - watermark_config.py / pip_config.py / intro_outro_config.py
   - reverse_engine.py
2. 治标: 调用方直接 .get() 处加 isinstance 防护
   - unified_render_service.py: tts/bgm/title/subtitle/export/bgm
   - render_adapter.py: bgm/export/title
   - render_audio.py: bgm/audio_tracks
   - generation.py: title/subtitle/bgm/export
   - edit_plan_generation.py: title

共修复 12 个文件，覆盖渲染管线全部 unprotected 调用点

apps/worker/video_processing/render_adapter.py

@@ -81,7 +81,9 @@ class RenderAdapterResult:
     failed_clip_ids: list[str] = None  # 失败的 clip id 列表
     error_message: str = ""
     error_detail: str = ""  # 详细错误信息（如 ffmpeg stderr），用于排查
-    cover_url: str = ""  # 封面图片 URL（从渲染后视频抽帧，天然带标题）
+    cover_candidates: list[dict] | None = (
+        None  # 封面候选帧 [{"image_url": "...", "frame_time": 5.0, "storage_key": "..."}]
+    )
 
     def __post_init__(self):
         if self.rendered_clip_ids is None:
@@ -517,6 +519,8 @@ class RenderAdapter:
 
         # 3. 读取输出分辨率
         export_config = plan_config.get("export", {}) or {}
+        if not isinstance(export_config, dict):
+            export_config = {}
         output_width, output_height = _parse_resolution(export_config.get("resolution"))
         logger.info(
             "渲染输出分辨率: plan_id=%s resolution=%dx%d source=%s",
@@ -560,33 +564,45 @@ class RenderAdapter:
         storage_key = f"rendered/{plan_id}/{job_id or plan_id}.mp4"
         output_url = upload_to_oss(result.output_path, storage_key)
 
-        self._report_progress(progress_cb, 90.0, "抽取封面帧")
+        self._report_progress(progress_cb, 90.0, "生成封面缩略图")
 
-        # 6. 从已渲染视频抽取封面帧（标题已通过 ASS 字幕烧录，封面天然带标题）
-        cover_url = ""
-        cover_frame_path = None
+        # 6. 生成封面缩略图
+        thumbnail_url = ""
         try:
-            from video_processing.thumbnail_generator import extract_first_frame
+            from video_processing.thumbnail_generator import generate_and_upload_thumbnail
 
-            cover_frame_path = extract_first_frame(str(result.output_path), width=640)
-            cover_storage_key = f"rendered/{plan_id}/cover.jpg"
-            try:
-                cover_url = upload_to_oss(cover_frame_path, cover_storage_key) or ""
-            finally:
-                if cover_frame_path:
-                    try:
-                        Path(cover_frame_path).unlink(missing_ok=True)
-                    except Exception:
-                        pass
-            if cover_url:
+            thumb_storage_key = f"rendered/{plan_id}/thumbnail.jpg"
+            thumbnail_url = generate_and_upload_thumbnail(str(result.output_path), thumb_storage_key)
+        except Exception as thumb_err:
+            logger.warning(
+                "[render-adapter] 缩略图生成失败（不影响主流程）: plan_id=%s error=%s",
+                plan_id,
+                thumb_err,
+            )
+
+        # 7. 抽取封面候选帧并上传 OSS（失败不阻断主流程）
+        cover_candidates = None
+        try:
+            from video_processing.thumbnail_generator import extract_and_upload_cover_frames
+
+            # 从 plan config 提取标题文字，叠加到封面候选帧上
+            _title_cfg = (plan_config or {}).get("title", {}) or {}
+            if not isinstance(_title_cfg, dict):
+                _title_cfg = {}
+            _title_text = (_title_cfg.get("text", "") or "").strip() if _title_cfg.get("enabled", True) else ""
+
+            cover_candidates = extract_and_upload_cover_frames(
+                str(result.output_path), plan_id, num_frames=3, title_text=_title_text
+            )
+            if cover_candidates:
                 logger.info(
-                    "[render-adapter] 封面帧提取成功: plan_id=%s url=%s",
+                    "[render-adapter] 封面候选帧生成成功: plan_id=%s count=%d",
                     plan_id,
-                    cover_url[:80],
+                    len(cover_candidates),
                 )
         except Exception as cover_err:
             logger.warning(
-                "[render-adapter] 封面帧提取失败（不影响主流程）: plan_id=%s error=%s",
+                "[render-adapter] 封面候选帧生成失败（不影响主流程）: plan_id=%s error=%s",
                 plan_id,
                 cover_err,
             )
@@ -614,7 +630,7 @@ class RenderAdapter:
             success=True,
             output_url=output_url or "",
             output_path=result.output_path,
-            thumbnail_url=cover_url,
+            thumbnail_url=thumbnail_url,
             duration=result.duration,
             file_size=result.file_size,
             width=result.width,
@@ -622,7 +638,7 @@ class RenderAdapter:
             clip_count=len(clips),
             rendered_clip_ids=final_rendered_ids,
             failed_clip_ids=final_failed_ids,
-            cover_url=cover_url,
+            cover_candidates=cover_candidates,
         )
 
     def render_from_memory(