fix(deploy): increase OCR healthcheck start_period, comment ocr_cache volume, add token hint

- start_period 60s → 120s: Zenodo download on cold start can exceed 60s on slow connections
- ocr_cache volume comment: documents what the cache stores for future operators
- .env.example: add token generation command to prevent weak placeholder in production

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

docker-compose.yml

@@ -87,7 +87,7 @@ services:
     memswap_limit: 12g
     volumes:
       - ocr_models:/app/models
-      - ocr_cache:/root/.cache
+      - ocr_cache:/root/.cache  # Hugging Face / ketos model download cache — prevents re-downloads on container recreate
     environment:
       KRAKEN_MODEL_PATH: /app/models/german_kurrent.mlmodel
       TRAINING_TOKEN: "${OCR_TRAINING_TOKEN:-}"
@@ -102,7 +102,7 @@ services:
       interval: 10s
       timeout: 5s
       retries: 12
-      start_period: 60s
+      start_period: 120s
 
   # --- Backend: Spring Boot ---
   backend: