ops(gpu-health): GPU 서비스 health/smoke 표준화 + synthetic VRAM 피크 가드

PR-GPU-Health-1. 운영 준비성 표준화 PR (모델 성능 개선 아님).

- OCR /smoke endpoint 추가 (160x60 OK PNG in-memory, 200/503 분기, Docker healthcheck 미사용)
- marker /health endpoint 추가 (stt/ocr 동일 시그니처)
- reranker docker-compose healthcheck 추가 (TEI :80/health)
- scripts/gpu_service_smoke.sh: docker exec 표준 점검 (OCR/STT expose-only)
- scripts/gpu_vram_fixture.sh: Mode A sequential + Mode B light overlap + --stress 옵션
- tests/load/fixtures/: synthetic ocr_ok.png / sine_30s.wav / lorem_1p.pdf

OCR 빈 응답 false negative — root cause: ports 미매핑.
결정: ocr-service / stt-service 는 expose-only 유지, 운영 점검은 docker exec 내부 curl 표준.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -149,6 +149,12 @@ services:
             - driver: nvidia
               count: 1
               capabilities: [gpu]
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://localhost/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 120s
     restart: unless-stopped
 
   ai-gateway: