Implement Phase 22: REST API (FastAPI + SSE streaming)

- api.py: FastAPI 앱 신규 생성
  - GET /health, POST /chat (SSE), POST /reset, POST /ingest, GET/DELETE /documents
  - SSE 포맷: data: <JSON 토큰>\n\n / data: [DONE]\n\n
  - Bearer Token 인증 (API_TOKEN 미설정 시 개발 모드)
  - user_id 파라미터로 멀티유저 지원 (기존 AgentService·DB 구조 재사용)
- config.py: api_token 필드 추가
- app.py: _get_agent에 query_rewrite_enabled 누락 수정
- requirements.txt: fastapi, uvicorn[standard], python-multipart 추가
- ROADMAP: Phase 22 ✅, Telegram Bot 클라이언트 예시 추가

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api.py

@@ -0,0 +1,128 @@
+"""율봇 REST API — Phase 22.
+
+실행:
+    uvicorn api:app --host 0.0.0.0 --port 8000
+
+클라이언트 예시:
+    import httpx, json
+    headers = {"Authorization": "Bearer YOUR_TOKEN"}
+    with httpx.Client() as c:
+        with c.stream("POST", "http://localhost:8000/chat",
+                      json={"message": "안녕", "user_id": "홍길동"},
+                      headers=headers, timeout=120) as r:
+            for line in r.iter_lines():
+                if line.startswith("data: ") and line != "data: [DONE]":
+                    print(json.loads(line[6:]), end="", flush=True)
+"""
+import json
+import os
+import tempfile
+
+from dotenv import load_dotenv
+load_dotenv()
+
+from fastapi import Depends, FastAPI, File, Header, HTTPException, UploadFile
+from fastapi.responses import StreamingResponse
+from pydantic import BaseModel
+
+from container import Container
+from services.agent.agent_service import AgentService
+
+app = FastAPI(title="율봇 API", version="1.0")
+
+_container = Container()
+_container.db_service().connect()
+_container.db_service().init_schema()
+
+_cfg = _container.config()
+_agent_cache: dict[str, AgentService] = {}
+
+
+def _get_agent(user_id: str) -> AgentService:
+    if user_id not in _agent_cache:
+        _agent_cache[user_id] = AgentService(
+            chat_model=_container.chat_model(),
+            retriever_service=_container.retriever_service(),
+            system_prompt=_cfg.system_prompt,
+            rag_verbose=_cfg.rag_verbose,
+            rag_show_sources=_cfg.rag_show_sources,
+            langgraph_verbose=_cfg.langgraph_verbose,
+            think_verbose=_cfg.think_verbose,
+            query_rewrite_enabled=_cfg.query_rewrite_enabled,
+            user_profile_repository=_container.user_profile_repository(),
+            conversation_repository=_container.conversation_repository(),
+            user_id=user_id,
+        )
+    return _agent_cache[user_id]
+
+
+def _auth(authorization: str = Header(default="")):
+    """API_TOKEN 설정 시 Bearer 토큰 검증. 미설정 시 인증 스킵(개발 모드)."""
+    token = _cfg.api_token
+    if token and authorization != f"Bearer {token}":
+        raise HTTPException(status_code=401, detail="Unauthorized")
+
+
+# ── 요청/응답 모델 ────────────────────────────────────────────
+
+
+class ChatRequest(BaseModel):
+    message: str
+    user_id: str = "default"
+    show_thinking: bool = False
+
+
+# ── 엔드포인트 ────────────────────────────────────────────────
+
+
+@app.get("/health")
+async def health():
+    return {"status": "ok"}
+
+
+@app.post("/chat")
+async def chat(req: ChatRequest, _=Depends(_auth)):
+    """SSE 스트리밍 응답. 각 라인: `data: <JSON 토큰>\n\n`, 종료: `data: [DONE]\n\n`"""
+    agent = _get_agent(req.user_id)
+
+    async def generate():
+        async for token in agent.stream_response(req.message, show_thinking=req.show_thinking):
+            yield f"data: {json.dumps(token, ensure_ascii=False)}\n\n"
+        yield "data: [DONE]\n\n"
+
+    return StreamingResponse(generate(), media_type="text/event-stream")
+
+
+@app.post("/reset")
+async def reset(user_id: str = "default", _=Depends(_auth)):
+    """대화 이력 초기화."""
+    if user_id in _agent_cache:
+        _agent_cache[user_id].reset()
+    return {"reset": True, "user_id": user_id}
+
+
+@app.post("/ingest")
+async def ingest(file: UploadFile = File(...), _=Depends(_auth)):
+    """PDF 또는 TXT 파일을 업로드해 벡터DB에 수집."""
+    suffix = os.path.splitext(file.filename or "")[1] or ".bin"
+    with tempfile.NamedTemporaryFile(delete=False, suffix=suffix) as f:
+        f.write(await file.read())
+        tmp_path = f.name
+    try:
+        count = _container.ingestion_service().ingest([tmp_path])
+        return {"chunks": count, "filename": file.filename}
+    finally:
+        os.unlink(tmp_path)
+
+
+@app.get("/documents")
+async def list_documents(_=Depends(_auth)):
+    """등록된 문서 경로 목록 반환."""
+    return {"documents": _container.retriever_service().list_documents()}
+
+
+@app.delete("/documents/{source:path}")
+async def delete_document(source: str, _=Depends(_auth)):
+    """source 경로에 해당하는 모든 청크 삭제."""
+    _container.retriever_service().delete_document(source)
+    return {"deleted": source}