refactor: remove all workspace_id references from codebase

- Remove workspace_id from Pydantic models in project_management routes
- Remove workspace_id from SQLAlchemy and SQLite project management repos
- Remove workspace_id from worker tasks (storage keys, entity creation)
- Remove workspace_id from video dedup and title usage modules
- Remove workspace_id from generation and ingest worker tasks
- Clean workspace_id from all test files and scripts
- Remove workspace-specific test files (list_workspaces, workspace repos)

Task: #14 workspace_id 残留清理

scripts/init_tracker_data.py

@@ -29,7 +29,6 @@ def create_milestone(name, target_date, description=""):
         "name": name,
         "target_date": target_date,
         "project_id": PROJECT_ID,
-        "workspace_id": WORKSPACE_ID,
         "description": description,
     }
     resp = requests.post(f"{API_BASE}/project-management/milestones", json=payload)
@@ -47,7 +46,6 @@ def create_task(name, description, priority="medium", status="pending", progress
         "name": name,
         "description": description,
         "project_id": PROJECT_ID,
-        "workspace_id": WORKSPACE_ID,
         "priority": priority,
     }
     resp = requests.post(f"{API_BASE}/project-management/tasks", json=payload)