调整项目库拆帧与长帧序列加载

- 删除项目库右上角独立新建项目入口，保留导入视频/DICOM 自动建项目流程

- 视频项目支持已生成帧后的重新生成帧入口，并提示会清空旧帧、标注和 mask

- 后端重新拆帧任务开始前清理旧帧、旧标注和旧 mask，避免重复帧序列

- 项目帧列表接口默认返回完整帧序列，避免工作区总帧数被 1000 条默认 limit 截断

- 增加可选 docker-compose.gpu.yml，并补充 Docker 使用本机 GPU 的前提和启动说明

- 更新项目库、API 映射、恢复演示文案、后端媒体/项目测试和前端文档

backend/services/media_task_runner.py

@@ -11,7 +11,7 @@ from typing import Any
 from sqlalchemy.orm import Session
 
 from minio_client import BUCKET_NAME, download_file, get_minio_client, upload_file
-from models import Frame, ProcessingTask, Project
+from models import Annotation, Frame, Mask, ProcessingTask, Project
 from progress_events import publish_task_progress_event
 from services.frame_parser import (
     extract_thumbnail,
@@ -109,6 +109,16 @@ def _frame_sequence_metadata(
     }
 
 
+def _clear_existing_project_outputs(db: Session, project: Project) -> None:
+    """Remove stale frame sequence and annotations before regenerating frames."""
+    annotation_ids = db.query(Annotation.id).filter(Annotation.project_id == project.id)
+    db.query(Mask).filter(Mask.annotation_id.in_(annotation_ids)).delete(synchronize_session=False)
+    db.query(Annotation).filter(Annotation.project_id == project.id).delete(synchronize_session=False)
+    db.query(Frame).filter(Frame.project_id == project.id).delete(synchronize_session=False)
+    project.thumbnail_url = None
+    db.commit()
+
+
 def _ensure_not_cancelled(db: Session, task: ProcessingTask) -> None:
     db.refresh(task)
     if task.status == TASK_STATUS_CANCELLED:
@@ -169,6 +179,7 @@ def run_parse_media_task(db: Session, task_id: int) -> dict[str, Any]:
 
     _ensure_not_cancelled(db, task)
     project.status = PROJECT_STATUS_PARSING
+    _clear_existing_project_outputs(db, project)
     _set_task_state(db, task, status=TASK_STATUS_RUNNING, progress=5, message="后台解析已启动", started=True)
 
     payload = task.payload or {}