feat: implement portfolio UUID migration and v1 API finalization (BAT-006, BAT-001 re-verified)

Core Changes:
- Migrate portfolio_id from string to UUID in schema and repository layer
- Update portfolio CLI commands to use name+user combination for identification
- Update HTTP API to accept portfolio_id as UUID path parameter
- Implement portfolio ownership validation in repository queries

Requirements Completed (REQ-016 to REQ-019):
- REQ-016: portfolios table UUID schema migration with data migration script
- REQ-017: CLI portfolio commands with name+user identification
- REQ-018: HTTP API portfolio path parameters and v1 asset_id UUID returns
- REQ-019: Portfolio UUID baseline documentation updates

BAT-001 Re-verification:
- REQ-004~010 marked as Implemented after verification evidence validation
- All v1 API endpoints verified with comprehensive test coverage

Documentation Updates:
- Update data-model.md with portfolio UUID structure
- Update interface-contract.md with UUID path parameters
- Update runtime-flows.md with ownership-based resolution flows
- Update project-structure.md with database layer changes
- Add migration script for portfolio UUID transition

Testing:
- Add test_portfolio_uuid.py for migration validation
- Update test_cli.py and test_portfolio_ownership.py for ownership checks

tests/test_portfolio_ownership.py

@@ -164,7 +164,7 @@ def test_db_enabled_env_token_without_user_context_is_rejected(monkeypatch) -> N
     response = client.post(
         "/portfolios",
         headers={"Authorization": "Bearer trade-env-token"},
-        json={"portfolio_id": "new-1", "symbol": "005930"},
+        json={"name": "new-1", "symbol": "005930"},
     )
 
     app.dependency_overrides.clear()