fix: use service hostname for Grafana proxy

Use http://grafana:3000 (service discovery) instead of localhost:3000. This works in both:
- Local dev: docker-compose service name
- Railway: service-to-service networking

Author: scotty595

src/routes/grafana.ts

@@ -2,9 +2,13 @@ import type { FastifyPluginAsyncTypebox } from '@fastify/type-provider-typebox';
 import httpProxy from '@fastify/http-proxy';
 
 const grafanaRoutes: FastifyPluginAsyncTypebox = async (fastify) => {
-  // Proxy all /grafana requests to local Grafana instance
+  // Proxy all /grafana requests to Grafana service
+  // In Railway: add Grafana as a separate service, it will be available at http://grafana:3000
+  // In local dev: docker-compose provides grafana service at http://grafana:3000
+  const grafanaUrl = process.env.GRAFANA_URL || 'http://grafana:3000';
+  
   await fastify.register(httpProxy, {
-    upstream: 'http://localhost:3000',
+    upstream: grafanaUrl,
     prefix: '/grafana',
     rewritePrefix: '/',
     http2: false,