收敛用户角色并共享项目库

- 后端限制系统只保留默认 admin 管理员，新建用户固定为标注员，并拒绝观察员或额外管理员角色。

- 将项目、帧、媒体解析、AI 标注、任务、Dashboard 和导出接口改为共享项目库访问，标注员具备同等项目管理和标注能力。

- 前端用户管理移除角色选择和观察员入口，只展示唯一管理员与标注员状态。

- 更新后端/前端测试，覆盖唯一 admin、旧 viewer 归一为标注员、用户删除和共享项目库访问。

- 同步更新 AGENTS 与 doc 文档中的角色权限、共享项目库和测试计划说明。

backend/routers/projects.py

@@ -16,12 +16,12 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/api/projects", tags=["Projects"])
 
 
-def _next_project_copy_name(db: Session, owner_user_id: int, source_name: str) -> str:
+def _next_project_copy_name(db: Session, source_name: str) -> str:
     base_name = f"{source_name} 副本"
     existing_names = {
         row[0]
         for row in db.query(Project.name)
-        .filter(Project.owner_user_id == owner_user_id, Project.name.like(f"{base_name}%"))
+        .filter(Project.name.like(f"{base_name}%"))
         .all()
     }
     if base_name not in existing_names:
@@ -76,7 +76,6 @@ def list_projects(
     """Retrieve a paginated list of projects."""
     projects = (
         db.query(Project)
-        .filter(Project.owner_user_id == current_user.id)
         .offset(skip)
         .limit(limit)
         .all()
@@ -97,10 +96,7 @@ def get_project(
     current_user: User = Depends(get_current_user),
 ) -> Project:
     """Retrieve a project by its ID."""
-    project = db.query(Project).filter(
-        Project.id == project_id,
-        Project.owner_user_id == current_user.id,
-    ).first()
+    project = db.query(Project).filter(Project.id == project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     return _prepare_project_response(project)
@@ -119,16 +115,13 @@ def copy_project(
     current_user: User = Depends(require_editor),
 ) -> Project:
     """Copy a project. Reset copies media/frame sequence; full also copies annotations and mask metadata."""
-    source = db.query(Project).filter(
-        Project.id == project_id,
-        Project.owner_user_id == current_user.id,
-    ).first()
+    source = db.query(Project).filter(Project.id == project_id).first()
     if not source:
         raise HTTPException(status_code=404, detail="Project not found")
 
     next_name = (payload.name or "").strip() if payload.name is not None else ""
     if not next_name:
-        next_name = _next_project_copy_name(db, current_user.id, source.name)
+        next_name = _next_project_copy_name(db, source.name)
 
     copied = Project(
         name=next_name,
@@ -196,10 +189,7 @@ def update_project(
     current_user: User = Depends(require_editor),
 ) -> Project:
     """Update project fields partially."""
-    project = db.query(Project).filter(
-        Project.id == project_id,
-        Project.owner_user_id == current_user.id,
-    ).first()
+    project = db.query(Project).filter(Project.id == project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
 
@@ -227,10 +217,7 @@ def delete_project(
     current_user: User = Depends(require_editor),
 ) -> None:
     """Delete a project and all related frames and annotations."""
-    project = db.query(Project).filter(
-        Project.id == project_id,
-        Project.owner_user_id == current_user.id,
-    ).first()
+    project = db.query(Project).filter(Project.id == project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
 
@@ -255,10 +242,7 @@ def create_frame(
     current_user: User = Depends(require_editor),
 ) -> Frame:
     """Register a new frame under a project."""
-    project = db.query(Project).filter(
-        Project.id == project_id,
-        Project.owner_user_id == current_user.id,
-    ).first()
+    project = db.query(Project).filter(Project.id == project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
 
@@ -282,10 +266,7 @@ def list_frames(
     current_user: User = Depends(get_current_user),
 ) -> List[Frame]:
     """Retrieve all frames belonging to a project."""
-    project = db.query(Project).filter(
-        Project.id == project_id,
-        Project.owner_user_id == current_user.id,
-    ).first()
+    project = db.query(Project).filter(Project.id == project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
 
@@ -320,7 +301,6 @@ def get_frame(
         .filter(
             Frame.project_id == project_id,
             Frame.id == frame_id,
-            Project.owner_user_id == current_user.id,
         )
         .first()
     )