fix(ssr): fetch station config during server-side rendering

The isPlatformBrowser guard in App.ngOnInit() was blocking
stationConfig.load() on the server, so SSR always rendered with
DEFAULT_CONFIG (hardcoded colors, assets, content).

Two-part fix:
- main.server.ts: Add APP_INITIALIZER that blocks server rendering
  until station config is fetched from the API. Only runs on the
  server — is a no-op in the browser to avoid blocking the client.
- app.ts: Move stationConfig.load() before the isPlatformBrowser
  guard so ngOnInit also calls it on the server as a safety net.

This ensures SSR HTML contains real DB values (colors, hero icon,
station name, etc.) instead of build-time defaults — eliminating
the stale-asset flash reported by users.

src/app/app.ts

@@ -54,14 +54,17 @@ export class App implements OnInit, OnDestroy {
   }
 
   ngOnInit(): void {
+    // Load station config on BOTH server and browser. On the server this
+    // fetches fresh data from the API so SSR renders with real colors,
+    // assets, and content — not DEFAULT_CONFIG baked at build time.
+    this.stationConfig.load().catch(() => {});
+
     // These DOM operations only run in the browser.
     if (!isPlatformBrowser(this.platformId)) return;
 
-    // Load runtime config.json and station config asynchronously in the
-    // background — do not block rendering. The app already renders with
-    // defaults from the SSR/prerendered HTML.
+    // Load runtime config.json asynchronously in the background — do not
+    // block rendering.
     loadAppConfigAsync(this.http).catch(() => {});
-    this.stationConfig.load().catch(() => {});
 
     // Start watching router for automatic SEO metadata updates per route.
     this.seoService.watchRouter();