refactor: replace mileage monolith with modular route files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/server/routes/mileage/index.ts

@@ -0,0 +1,18 @@
+import { Hono } from 'hono';
+import { refreshMonitoringCache } from './cache.js';
+import monitoringRouter from './monitoring.js';
+import targetsRouter from './targets.js';
+import trendRouter from './trend.js';
+
+const app = new Hono();
+
+app.route('/monitoring', monitoringRouter);
+app.route('/targets', targetsRouter);
+app.route('/target', targetsRouter);
+app.route('/trend', trendRouter);
+
+// 启动时立即刷新缓存，之后每分钟刷新
+refreshMonitoringCache();
+setInterval(refreshMonitoringCache, 60 * 1000);
+
+export default app;