refactor(ds): vestigial ai-gateway 폐기

예산캡 LLM 게이트웨이(2026-04-03 GPU 이관 최초 커밋부터 존재). config.ai.gateway 파싱만·소비코드 0줄·established 0·요청 이력 0 = vestigial 입증. docker-compose.yml ai-gateway 서비스블록 + config.yaml ai.gateway 블록 제거. 컨테이너+image(256MB) 제거, fastapi 무손상(재생성 안 함). dangling CLAUDE_API_KEY env 노출 동반 제거(credentials.env=gitignore 별도).

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

docker-compose.yml

@@ -168,19 +168,6 @@ services:
       start_period: 120s
     restart: unless-stopped
 
-  ai-gateway:
-    build: ./gpu-server/services/ai-gateway
-    ports:
-      - "127.0.0.1:8081:8080"
-    environment:
-      - PRIMARY_ENDPOINT=http://100.76.254.116:8801/v1/chat/completions
-      - FALLBACK_ENDPOINT=http://ollama:11434/v1/chat/completions
-      - CLAUDE_API_KEY=${CLAUDE_API_KEY:-}
-      - DAILY_BUDGET_USD=${DAILY_BUDGET_USD:-5.00}
-    # depends_on: ollama 제거 (2026-06-08) — ollama 서비스가 standalone 으로 이관됨.
-    # FALLBACK_ENDPOINT 의 ollama:11434 는 standalone(동일 hostname, DS 망 부착)으로 해소.
-    restart: unless-stopped
-
   fastapi:
     build: ./app
     ports: