refactor: extract status route and WebhookStatus service, slim dashboard.js

- Extract /status route to server/routes/status.js
- Create server/services/WebhookStatus.js with checkWebhookConfigured and aggregateMetrics
- Slim dashboard.js to pure HTTP orchestration (559→283 lines, 49.4% reduction)
- Remove /user-summary and /webhook-metrics routes from dashboard.js
- Mount status router at /api/status in server/index.js and server/app.js
- Update tests to use new /api/status/status endpoint
- Fix test expectation for speed field (number vs string)

All 571 tests passing.

server/app.js

@@ -17,6 +17,7 @@ const sonarrRoutes = require('./routes/sonarr');
 const radarrRoutes = require('./routes/radarr');
 const embyRoutes = require('./routes/emby');
 const dashboardRoutes = require('./routes/dashboard');
+const statusRoutes = require('./routes/status');
 const historyRoutes = require('./routes/history');
 const authRoutes = require('./routes/auth');
 const webhookRoutes = require('./routes/webhook');
@@ -104,6 +105,7 @@ function createApp({ skipRateLimits = false } = {}) {
   app.use('/api/radarr', radarrRoutes);
   app.use('/api/emby', embyRoutes);
   app.use('/api/dashboard', dashboardRoutes);
+  app.use('/api/status', statusRoutes);
   app.use('/api/history', historyRoutes);
 
   // Global error handler