fix(ssr): remove broken dynamic import and lazy-init engine

- Replace await import('./main.server.js') with lazy getEngine()
  (original path was wrong — main.server.ts lives in src/, not root)
- AngularNodeAppEngine handles manifest registration internally;
  no manual bootstrap import needed
- Add npm scripts: build:ssr, build:prerender, serve:ssr:radio-station
- Add PRERENDER.md build documentation

Verified: clean build prerenders all 5 routes, 54 tests pass

server.ts

@@ -21,8 +21,6 @@ export const PRERENDERED_ROUTES: readonly string[] = [
   '/contact',
 ];
 
-const ngApp = new AngularNodeAppEngine();
-
 /**
  * Normalise a request pathname and check against prerendered routes.
  * Handles both bare paths (`/about`) and trailing-slash variants (`/about/`).
@@ -35,6 +33,19 @@ export function isPrerenderedRoute(url: string): boolean {
   return PRERENDERED_ROUTES.includes(normalised);
 }
 
+/**
+ * Lazily instantiate AngularNodeAppEngine so the engine boots only when
+ * the first request arrives. The engine handles both prerendered route
+ * lookups and on-demand SSR bootstrapping internally.
+ */
+let appEngine: AngularNodeAppEngine | null = null;
+function getEngine(): AngularNodeAppEngine {
+  if (!appEngine) {
+    appEngine = new AngularNodeAppEngine();
+  }
+  return appEngine;
+}
+
 /**
  * Handle incoming requests using the Angular SSR engine.
  *
@@ -46,12 +57,14 @@ export default createNodeRequestHandler(async (req, res, next) => {
   try {
     const prerendered = isPrerenderedRoute(req.url || '/');
     if (prerendered) {
-      // Prerendered routes are served as static HTML — AngularNodeAppEngine
-      // reads the build-time manifest and returns the pre-generated response.
       console.log(`[SSR] Prerendered route: ${req.url}`);
     }
 
-    const response = await ngApp.handle(req);
+    // AngularNodeAppEngine handles manifest registration internally —
+    // no manual bootstrap import needed. For prerendered routes it
+    // returns pre-generated static HTML; for SSR routes it bootstraps
+    // the Angular app on demand.
+    const response = await getEngine().handle(req);
 
     if (response) {
       await writeResponseToNodeResponse(response, res);