fix: increase backend Docker healthcheck start_period to 3 minutes (refs #64)

The CI was failing because Docker marked the backend unhealthy before the CI
wait loop completed. The backend needs time to run migrations and seed vehicle
data on startup.

Changes:
- start_period: 40s -> 180s (3 minutes)
- retries: 3 -> 5 (more tolerance)

Total time before unhealthy: 180s + (5 × 30s) = 5.5 minutes

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -140,8 +140,8 @@ services:
         - node -e "require('http').get('http://localhost:3001/health', r => process.exit(r.statusCode===200?0:1)).on('error', () => process.exit(1))"
       interval: 30s
       timeout: 10s
-      retries: 3
-      start_period: 40s
+      retries: 5
+      start_period: 180s
     labels:
       - "traefik.enable=true"
       - "traefik.docker.network=motovaultpro_backend"