feat: add clickable links to daily digest emails via APP_URL

- Read APP_URL and AGRARMONITOR_BASE_URL from config
- Render dashboard entries as clickable links in HTML digest email
- Add APP_URL and DAILY_DIGEST_CRON to .env.example and docker-compose.yml

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

docker-compose.yml

@@ -47,6 +47,8 @@ services:
       - AGRARMONITOR_ENCRYPTION_KEY=${AGRARMONITOR_ENCRYPTION_KEY:-}
       - AGRARMONITOR_POLLING_CRON=${AGRARMONITOR_POLLING_CRON:-}
       - AGRARMONITOR_UPLOAD_CHECK_CRON=${AGRARMONITOR_UPLOAD_CHECK_CRON:-}
+      - APP_URL=${APP_URL:-}
+      - DAILY_DIGEST_CRON=${DAILY_DIGEST_CRON:-}
     volumes:
       - /mnt/scans:/mnt/scans
       - /mnt/paperlessmanager:/mnt/data