fix(ssr): prefer index.csr.html over prerendered index.html for CSR users

The browserIndexPath() function was resolving index.html first, which is
the prerendered output with stale build-time content baked into <app-root>.
Even with window.__STATION_CONFIG injection, the prerendered innerHTML
still shows old content on the first paint until Angular re-renders.

By preferring index.csr.html (the pure CSR shell with empty <app-root>),
regular users get a clean first paint — no stale prerendered DOM to flash.

server.ts

@@ -72,7 +72,17 @@ const COLOR_MAP: ReadonlyArray<{ field: keyof StationConfig; prop: string }> = [
 ];
 
 /**
- * Resolve the static browser index.html path.
+ * Resolve the static CSR shell path (index.csr.html).
+ *
+ * IMPORTANT: We MUST prefer index.csr.html over index.html.
+ * The Angular build with prerender config produces both:
+ * - index.html: prerendered at build time with stale DEFAULT_CONFIG baked in
+ * - index.csr.html: pure CSR shell with empty <app-root> — Angular hydrates client-side
+ *
+ * Serving index.html to regular users causes the flash: the prerendered DOM
+ * shows stale build-time content until Angular re-renders with fresh data.
+ * Even with window.__STATION_CONFIG injection, the prerendered innerHTML inside
+ * <app-root> still shows old content on the first paint.
  *
  * Production (Docker): browser files are copied to /usr/share/nginx/html/
  * Local dev (ng build): browser files live in dist/radio-station/browser/
@@ -80,9 +90,11 @@ const COLOR_MAP: ReadonlyArray<{ field: keyof StationConfig; prop: string }> = [
  */
 function browserIndexPath(): string {
   // Production path — Dockerfile copies browser output here
+  // CSR shell first — avoid prerendered index.html with stale content
   const productionPaths = [
-    '/usr/share/nginx/html/index.html',
     '/usr/share/nginx/html/index.csr.html',
+    '/usr/share/nginx/html/index.html',
+    '/var/www/html/index.csr.html',
     '/var/www/html/index.html',
   ];