Add structured JSON logging, OTel business metrics, and Grafana dashboard

Structured logging via JsonFormatter replaces uvicorn's default format so
Loki can parse timestamps and fields.  14 business metrics (scrape stats,
throttle events, circuit breaker state, cache hit rate, OCR success rate,
Celery task lifecycle) are defined in a shared metrics module and
instrumented across the scraper pipeline, API, and workers.  Celery
workers expose a Prometheus HTTP endpoint on configurable ports.

docker-compose.yml

@@ -51,6 +51,7 @@ services:
       - app_venv:/app/.venv
     environment:
       - ENV=dev
+      - SERVICE_NAME=api
       - DB_CONNECTION_STRING=mysql+mysqldb://wrongmove:wrongmove@mysql:3306/wrongmove
       - CELERY_BROKER_URL=redis://redis:6379/0
       - CELERY_RESULT_BACKEND=redis://redis:6379/0
@@ -74,11 +75,15 @@ services:
       context: .
       dockerfile: Dockerfile
     container_name: rec-celery
+    ports:
+      - "9090:9090"
     volumes:
       - .:/app
       - app_venv:/app/.venv
     environment:
       - ENV=dev
+      - SERVICE_NAME=celery-worker
+      - CELERY_METRICS_PORT=9090
       - DB_CONNECTION_STRING=mysql+mysqldb://wrongmove:wrongmove@mysql:3306/wrongmove
       - CELERY_BROKER_URL=redis://redis:6379/0
       - CELERY_RESULT_BACKEND=redis://redis:6379/0
@@ -98,11 +103,15 @@ services:
       context: .
       dockerfile: Dockerfile
     container_name: rec-celery-beat
+    ports:
+      - "9091:9091"
     volumes:
       - .:/app
       - app_venv:/app/.venv
     environment:
       - ENV=dev
+      - SERVICE_NAME=celery-beat
+      - CELERY_METRICS_PORT=9091
       - DB_CONNECTION_STRING=mysql+mysqldb://wrongmove:wrongmove@mysql:3306/wrongmove
       - CELERY_BROKER_URL=redis://redis:6379/0
       - CELERY_RESULT_BACKEND=redis://redis:6379/0