LLM 호출 규격 전환: 고객사 사내 LLM(FabriX/Gauss) 헤더 지원 (LLM_PROVIDER=fabrix)

- settings: LLM_PROVIDER/LLM_CHAT_PATH/LLM_BODY_MODEL/LLM_JSON_MODE/LLM_MAX_TOKENS, FABRIX_* 3종, llm_enabled()
- llm_client: headers()/body() 를 규격별로 구성. fabrix 는 x-openapi-token(Bearer)/x-generative-ai-client/
  x-llm-model-id/x-generative-ai-user-email, body model 은 LLM_BODY_MODEL
- summarize/ping: 접속 점검 명령 (--show 로 요청만 확인)
- docs/llm-provider-plan.md: 계획·.env 값·오류별 조치. 기본값은 openai 라 기존 동작 불변

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

query/api.py

@@ -142,7 +142,7 @@ def ingest(payload: dict = Body(), background_tasks: BackgroundTasks = None) ->
     # SUMMARIZE_BACKEND=file 이면 키 없이 프롬프트만 큐에 쌓는다 (/summaries/jobs 로 확인).
     backend = settings.summarize_backend
     summarize = "disabled"
-    if backend != "off" and (backend == "file" or (settings.llm_base_url and settings.llm_api_key)):
+    if backend != "off" and (backend == "file" or settings.llm_enabled()):
         if status == "loaded" or pending:
             with _summarizing_lock:
                 already = program in _summarizing
@@ -328,7 +328,7 @@ def summaries_status() -> dict:
             running = sorted(_summarizing)
         return {
             "model": settings.llm_model,
-            "llm_enabled": bool(settings.llm_base_url and settings.llm_api_key),
+            "llm_enabled": settings.llm_enabled(),
             "running": running,
             "programs": per_program,
             "failures": failures,
@@ -392,7 +392,7 @@ def _persist_env(key: str, value: str) -> None:
 def get_llm_settings() -> dict:
     return {
         "model": settings.llm_model,
-        "enabled": bool(settings.llm_base_url and settings.llm_api_key),
+        "enabled": settings.llm_enabled(),
     }