chore: update Docker and compose files for PaddleOCR engine (refs #119)

- Replace libtesseract-dev with libgomp1 (OpenMP for PaddlePaddle)
- Pre-download PP-OCRv4 models during Docker build
- Add OCR engine env vars to all compose files (base, staging, prod)
- Add optional Google Vision secret mount (commented, enable on demand)
- Create google-vision-key.json.example placeholder

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

docker-compose.staging.yml

@@ -63,6 +63,15 @@ services:
   mvp-ocr:
     image: ${OCR_IMAGE:-git.motovaultpro.com/egullickson/ocr:latest}
     container_name: mvp-ocr-staging
+    environment:
+      LOG_LEVEL: debug
+      REDIS_HOST: mvp-redis
+      REDIS_PORT: 6379
+      REDIS_DB: 1
+      OCR_PRIMARY_ENGINE: paddleocr
+      OCR_FALLBACK_ENGINE: ${OCR_FALLBACK_ENGINE:-none}
+      OCR_FALLBACK_THRESHOLD: ${OCR_FALLBACK_THRESHOLD:-0.6}
+      GOOGLE_VISION_KEY_PATH: /run/secrets/google-vision-key.json
 
   # ========================================
   # PostgreSQL (Staging - Separate Database)