feat: implement full RBAC role-based access control

Backend:
- deps.py: add require_admin, require_manager, require_labeler, require_guest_or_above
- user.py: all write endpoints require admin
- datasource.py: write/sync endpoints require admin
- metadata.py: sync endpoint requires admin
- classification.py: category/rule write requires admin; results query requires guest+ with data isolation
- project.py: GET requires manager with created_by filtering; DELETE checks ownership
- task.py: my-tasks requires labeler with assignee_id filtering; create-task requires manager
- dashboard.py: requires guest_or_above
- report.py: requires guest_or_above
- project_service: list_projects adds created_by filter; list_results adds project_ids filter

Frontend:
- stores/user.ts: add hasRole, hasAnyRole, isAdmin, isManager, isLabeler, isSuperadmin
- router/index.ts: add roles to route meta; beforeEach checks role permissions
- Layout.vue: filter menu routes by user roles
- System.vue: hide add/edit/delete buttons for non-admins
- DataSource.vue: hide add/edit/delete/sync buttons for non-admins
- Project.vue: hide add/delete buttons for non-admins

backend/app/api/v1/task.py

@@ -5,7 +5,7 @@ from sqlalchemy.orm import Session
 from app.core.database import get_db
 from app.models.user import User
 from app.schemas.common import ResponseModel, ListResponse
-from app.api.deps import get_current_user
+from app.api.deps import get_current_user, require_manager, require_labeler, _is_admin
 from app.services import task_service, project_service
 
 router = APIRouter()
@@ -15,9 +15,11 @@ router = APIRouter()
 def my_tasks(
     status: Optional[str] = Query(None),
     db: Session = Depends(get_db),
-    current_user: User = Depends(get_current_user),
+    current_user: User = Depends(require_labeler),
 ):
-    items, _ = task_service.list_tasks(db, assignee_id=current_user.id, status=status)
+    # Data isolation: non-admin users only see tasks assigned to them
+    assignee_id = None if _is_admin(current_user) else current_user.id
+    items, _ = task_service.list_tasks(db, assignee_id=assignee_id, status=status)
     data = []
     for t in items:
         project = project_service.get_project(db, t.project_id)
@@ -100,7 +102,7 @@ def create_task_for_project(
     assignee_id: int,
     target_type: str = Query("column"),
     db: Session = Depends(get_db),
-    current_user: User = Depends(get_current_user),
+    current_user: User = Depends(require_manager),
 ):
     task = task_service.create_task(
         db, project_id=project_id, name=name,