feat(maturity): add dedicated NSFW/maturity analysis service

- Add maturity/ service (FastAPI + Falconsai/nsfw_image_detection ViT classifier)
  - /analyze (URL) and /analyze/file (multipart upload) endpoints
  - Normalized response: maturity_label, confidence, score, labels,
    action_hint (safe/review/flag_high), advisory, threshold_used,
    analysis_time_ms, model, source
  - Configurable thresholds via MATURITY_THRESHOLD_MATURE / MATURITY_THRESHOLD_REVIEW
  - Reuses common/image_io for URL validation and file-size enforcement
  - Explicit 502/503 errors on failure — no silent safe fallback
  - Per-request structured logging (score, label, threshold path, elapsed ms)

- Update gateway/main.py
  - MATURITY_URL + MATURITY_ENABLED env vars
  - POST /analyze/maturity and POST /analyze/maturity/file endpoints
  - /health includes maturity service status
  - _assert_maturity_enabled() guard for clean 503 when disabled
  - All existing endpoints untouched (additive change)

- Update docker-compose.yml
  - Add maturity service with healthcheck (start_period: 90s)
  - Gateway environment: MATURITY_URL, MATURITY_ENABLED
  - Gateway depends_on: maturity (service_healthy)

- Update README.md and USAGE.md
  - Document maturity service, env vars, curl examples,
    full response schema table, action_hint logic, failure guidance

docker-compose.yml

@@ -13,6 +13,8 @@ services:
       - YOLO_URL=http://yolo:8000
       - QDRANT_SVC_URL=http://qdrant-svc:8000
       - CARD_RENDERER_URL=http://card-renderer:8000
+      - MATURITY_URL=http://maturity:8000
+      - MATURITY_ENABLED=true
       - API_KEY=${API_KEY}
       - VISION_TIMEOUT=300
       - MAX_IMAGE_BYTES=52428800
@@ -27,6 +29,8 @@ services:
         condition: service_healthy
       card-renderer:
         condition: service_healthy
+      maturity:
+        condition: service_healthy
     healthcheck:
       test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8000/health', timeout=5).read()"]
       interval: 30s
@@ -131,3 +135,19 @@ services:
       retries: 5
       start_period: 60s
 
+  maturity:
+    build:
+      context: .
+      dockerfile: maturity/Dockerfile
+    environment:
+      - MATURITY_MODEL=${MATURITY_MODEL:-Falconsai/nsfw_image_detection}
+      - MATURITY_THRESHOLD_MATURE=${MATURITY_THRESHOLD_MATURE:-0.80}
+      - MATURITY_THRESHOLD_REVIEW=${MATURITY_THRESHOLD_REVIEW:-0.60}
+      - MAX_IMAGE_BYTES=52428800
+    healthcheck:
+      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8000/health', timeout=5).read()"]
+      interval: 30s
+      timeout: 10s
+      retries: 5
+      start_period: 90s
+