feat: extract OCR worker into separate service

- Remove Python/OCR steps from backend.Dockerfile (builder + runtime)
- Remove Python/OCR steps from backend-dev.Dockerfile
- Add OCR_BASE_URL env var to both Dockerfiles (http://ocr-worker:8100)
- Add ocr-worker service to docker-compose.yml with healthcheck
- Add ocr-worker service to docker-compose.dev.yml with healthcheck + port
- Update backend depends_on in both compose files to include ocr-worker
- Replace OCR_PROJECT_ROOT with OCR_BASE_URL in compose env vars
- Remove pip install line from start-dev-container.sh

apps/backend/scripts/start-dev-container.sh

@@ -85,7 +85,6 @@ start_browser_debug_services() {
 }
 
 npm install --no-fund --no-audit
-python3 -m pip install --no-cache-dir --break-system-packages -e /app/subservices/ocr-worker
 
 if ! is_true "${TENCENT_BROWSER_HEADLESS:-true}"; then
   start_browser_debug_services