refactor: make user_id a required input, drop hardcoded jsahn default

user_id is now a required workflow_dispatch input (no default) and the
runner validates it is non-empty before doing anything. Removed the
'jsahn' default from the script arg and replaced jsahn with <user_id>
placeholders throughout TEST_WORKFLOW.md so the workflow is not pinned
to one account.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

TEST_WORKFLOW.md

@@ -34,7 +34,7 @@ GITEA_TOKEN=<Gitea Personal Access Token>
 `.env` 의 토큰을 읽어 `workflow_dispatch` 를 호출한다. **토큰을 화면에 출력하지 말 것.**
 
 ```bash
-cd /Users/jsahn/Works/Liti-agent-Development
+cd <repo root>                    # 이 저장소 루트
 set -a; . ./.env; set +a          # .env 로드 ($GITEA_TOKEN)
 
 curl -s -X POST \
@@ -46,7 +46,7 @@ curl -s -X POST \
     "inputs": {
       "yaml_path": "Case_02_Comparison_Research/YAML_Prompts/1. Stage_1/v.5/Stage_1_Part_1.yml",
       "workspace_name": "팬아웃 테스트",
-      "user_id": "jsahn"
+      "user_id": "<user_id>"
     }
   }'
 # 성공 시 HTTP 204 (본문 없음)
@@ -88,7 +88,7 @@ pip install httpx httpx-sse
 python scripts/run_agent_api.py \
   --yaml-path="Case_02_Comparison_Research/YAML_Prompts/1. Stage_1/v.5/Stage_1_Part_1.yml" \
   --workspace-name="팬아웃 테스트" \
-  --user-id="jsahn" \
+  --user-id="<user_id>" \
   --api-base="http://100.93.221.71:8800" \
   --output-dir=agent_run_output
 ```
@@ -106,7 +106,7 @@ python scripts/run_agent_api.py \
 | `yaml_path` | ✅ | — | 실행할 Agent YAML 의 repo 상대경로 |
 | `workspace_name` | △ | `""` | 작업실 이름 → `GET /workspaces/lookup` 으로 UUID 해석 |
 | `workspace_id` | △ | `""` | 작업실 UUID 직접 지정(override). 비우면 name 으로 해석 |
-| `user_id` | | `jsahn` | AgentBackend user_id |
+| `user_id` | ✅ | — | AgentBackend user_id (실행 계정) |
 | `user_input` | | `""` | Agent 에 전달할 user_input |
 | `start_stage_index` | | `0` | 시작 stage 인덱스 |
 | `api_base` | | `http://agent-backend:8000` | 내부 컨테이너 주소 (/api 접두사 없음) |
@@ -116,7 +116,7 @@ python scripts/run_agent_api.py \
 
 작업실 이름↔UUID 목록 확인:
 ```bash
-curl -s "http://100.93.221.71:8800/workspaces/lookup?user_id=jsahn" | python3 -m json.tool
+curl -s "http://100.93.221.71:8800/workspaces/lookup?user_id=<user_id>" | python3 -m json.tool
 ```
 
 ---