feat: 统一预览与确认生成渲染路径 — 预览=正式品质+确认复用

## 渲染管线统一
- UnifiedRenderService: 移除 is_preview 参数，统一 CRF 23 + medium preset
- RenderAdapter: 移除 is_preview 参数，统一执行校验和缩略图生成
- Worker generation.py: 移除 480p+1M 码率覆盖逻辑
- generation_preview.py: 删除 PREVIEW_RESOLUTION 常量和 _calc_preview_resolution()

## 确认生成复用预览产物
- Domain: 新增 GenerationTask.mark_confirmed() 方法
- confirm_generation: 预览已完成时直接复用产物（秒出），无需重新渲染
- Editor generate: 检查 plan 关联的预览任务，plan未修改时复用产物
- Schema: CreatePreviewGenerationTaskRequest 新增 source_edit_plan_id 字段

## 测试更新
- test_1280_preview_speedup: 重写为验证统一品质参数
- test_confirm_generation: 重写为验证复用逻辑

## 交付标准
- 预览渲染质量与确认生成一致（1080p, CRF 23, medium）
- 预览后确认生成直接复用产物（秒出）
- Worker 端无任何 is_preview 低质量渲染代码残留

apps/worker/video_processing/render_adapter.py

@@ -485,7 +485,6 @@ class RenderAdapter:
         rendered_clip_ids: list[str] | None = None,
         failed_clip_ids: list[str] | None = None,
         voiceover_audio_path: str | None = None,
-        is_preview: bool = False,
     ) -> RenderAdapterResult:
         """执行统一渲染核心流程（BGM + ASR + 渲染 + 缩略图 + 上传）。
 
@@ -508,7 +507,7 @@ class RenderAdapter:
         # 预览模式下，如果 plan.config 中存在 voice_id，仍需初始化 ASR 以支持配音
         plan_config = plan.config or {}
         has_voice_id = bool(plan_config.get("voice_id"))
-        asr_service = None if (is_preview and not has_voice_id) else self._get_asr_service()
+        asr_service = self._get_asr_service()
 
         # 3. 读取输出分辨率
         export_config = plan_config.get("export", {}) or {}
@@ -532,27 +531,23 @@ class RenderAdapter:
             bgm_path=bgm_path,
             asr_service=asr_service,
             voiceover_audio_path=voiceover_audio_path,
-            is_preview=is_preview,
         )
         result = render_svc.render()
 
-        # 4.5 渲染后校验输出完整性（预览模式跳过，节省耗时）
-        if is_preview:
-            logger.info("[render-adapter] 预览模式：跳过输出校验")
-        else:
-            validation = validate_video_output(result.output_path)
-            if not validation.valid:
-                logger.error(
-                    "[render-adapter] 渲染输出校验失败: plan_id=%s job_id=%s error=%s",
-                    plan_id,
-                    job_id,
-                    validation.error_message,
-                )
-                return RenderAdapterResult(
-                    success=False,
-                    error_message=f"渲染输出校验失败: {validation.error_message}",
-                    error_detail=validation.error_message,
-                )
+        # 4.5 渲染后校验输出完整性
+        validation = validate_video_output(result.output_path)
+        if not validation.valid:
+            logger.error(
+                "[render-adapter] 渲染输出校验失败: plan_id=%s job_id=%s error=%s",
+                plan_id,
+                job_id,
+                validation.error_message,
+            )
+            return RenderAdapterResult(
+                success=False,
+                error_message=f"渲染输出校验失败: {validation.error_message}",
+                error_detail=validation.error_message,
+            )
         self._report_progress(progress_cb, 80.0, "上传渲染结果")
 
         # 5. 上传结果
@@ -561,20 +556,19 @@ class RenderAdapter:
 
         self._report_progress(progress_cb, 90.0, "生成封面缩略图")
 
-        # 6. 生成缩略图（预览模式跳过，节省耗时）
+        # 6. 生成封面缩略图
         thumbnail_url = ""
-        if not is_preview:
-            try:
-                from video_processing.thumbnail_generator import generate_and_upload_thumbnail
+        try:
+            from video_processing.thumbnail_generator import generate_and_upload_thumbnail
 
-                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,
-                )
+            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,
+            )
 
         self._report_progress(progress_cb, 100.0, "渲染完成")
 
@@ -620,7 +614,6 @@ class RenderAdapter:
         work_dir: Path | None = None,
         progress_cb: ProgressCallback | None = None,
         voiceover_audio_path: str | None = None,
-        is_preview: bool = False,
     ) -> RenderAdapterResult:
         """使用内存中的 plan/clips/asset_path_map 直接渲染。
 
@@ -679,7 +672,6 @@ class RenderAdapter:
                 job_id=job_id,
                 progress_cb=progress_cb,
                 voiceover_audio_path=voiceover_audio_path,
-                is_preview=is_preview,
             )
 
         except subprocess.CalledProcessError as exc: