fix: health check route via /api/health to match Traefik PathPrefix rule

/health is routed to frontend nginx by Traefik (no /api prefix).
Add /api/health alias so Traefik routes the check to the backend.
Update workflow healthcheck step to call /api/health.

backend/app/__init__.py

@@ -76,6 +76,7 @@ def create_app(config_name: str | None = None) -> Flask:
     app.register_blueprint(jobs_admin_bp)
 
     @app.route("/health")
+    @app.route("/api/health")
     def health():
         from flask import jsonify