feat(REQ-014): add portfolio-create-user-required requirement and implementation

- Add docs/srs/Interface/req-014_portfolio-create-user-required.md with acceptance criteria
- Create docs/batches/bat-004_20260502_portfolio-create-user-required/ delivery batch
- Enhance app/cli/commands/portfolio.py: validate user_id parameter before portfolio creation
- Add comprehensive CLI tests in tests/test_cli.py for portfolio create validation flows
- Update docs/batches/index.md and docs/srs/index.md with new requirement/batch references
- Update README.md documentation

docs/batches/bat-004_20260502_portfolio-create-user-required/planning.md

@@ -0,0 +1,50 @@
+# BAT-004 Planning
+
+- Status: confirmed
+- Batch: BAT-004
+- Profile: batch-lite
+
+## Included REQ
+
+- REQ-014: CLI `portfolio create --user` 필수화 및 소유자 설정
+
+## Out of Scope
+
+- HTTP API `POST /portfolios` owner 설정 변경
+- `owner_user_id` 기본값(`"system"`) 서비스 레이어 변경
+
+## 구현 순서
+
+### 1단계: CLI 명령 수정
+
+- `app/cli/commands/portfolio.py` — `create_portfolio` 명령 수정
+  - `user: str | None = typer.Option(None, "--user", help="Owner username (required).")` 추가
+  - `_with_service_and_repo` 콜백으로 교체
+  - callback 내부:
+    - `user is None` → `console.print(...)` + `raise typer.Exit(code=1)`
+    - `repository.get_user_by_username(user)` → `None`이면 `raise ValueError(...)`
+    - `service.create_portfolio(payload, owner_user_id=owner.id)` 호출
+
+### 2단계: README 수정
+
+- `README.md` — `pfhub portfolio create` 예제 라인에 `--user alice` 추가
+
+### 3단계: 테스트
+
+- `tests/test_cli.py`
+  - `test_cli_create_buy_and_delete_flow`: `--user alice` 추가, repo에 alice 생성
+  - `test_cli_write_command_prompts_before_create`: 동일 수정
+  - `test_cli_write_command_can_abort`: 동일 수정
+  - `test_cli_portfolio_create_without_user_exits_error` (신규)
+  - `test_cli_portfolio_create_with_valid_user_sets_owner` (신규)
+  - `test_cli_portfolio_create_with_unknown_user_exits_error` (신규)
+
+## Dependencies
+
+- Internal: `_with_service_and_repo` (BAT-003 도입, 이미 존재)
+- External: 없음
+
+## Design Gate
+
+- Design Required Before Implementation: no
+- Reason: 기존 `_with_service_and_repo` 패턴 재사용. 구조/스키마 변경 없음.