feat: add SSR and prerendering support

- Install @angular/ssr and @angular/platform-server (v21.2.x)
- Create server entry point (server.ts) and server bootstrap (main.server.ts)
- Add server routes config (app.server.routes.ts) with 5 prerendered routes:
  /, /about, /schedule, /events, /contact
- Update angular.json with server/ssr/prerender build configuration
- Add prerender-routes.txt for build-time static route generation
- Fix SSR compatibility:
  - App component: guard DOM access with isPlatformBrowser
  - StructuredDataComponent: skip head manipulation on server
  - ThemeService: skip CSS variable application on server
  - ShowService/EventService: return empty arrays on API failure
    (graceful fallback during prerender with no backend)
- Prerendered output verified: 5 static HTML routes in dist/

server.ts

@@ -0,0 +1,41 @@
+import {
+  AngularNodeAppEngine,
+  createNodeRequestHandler,
+  isMainModule,
+  writeResponseToNodeResponse,
+} from '@angular/ssr/node';
+import * as http from 'node:http';
+
+const ngApp = new AngularNodeAppEngine();
+
+/**
+ * Handle incoming requests using the Angular SSR engine.
+ * Prerendered routes are served as static HTML at build time.
+ * Dynamic routes fall back to server-side rendering.
+ */
+export default createNodeRequestHandler(async (req, res, next) => {
+  try {
+    const response = await ngApp.handle(req);
+    if (response) {
+      await writeResponseToNodeResponse(response, res);
+    } else {
+      next();
+    }
+  } catch (error) {
+    next(error);
+  }
+});
+
+if (isMainModule(import.meta.url)) {
+  const httpServer = http.createServer();
+  httpServer.on('request', async (req: http.IncomingMessage, res: http.ServerResponse) => {
+    const handler = (await import('./server.js')).default;
+    handler(req, res, () => {
+      res.statusCode = 404;
+      res.end('Not Found');
+    });
+  });
+  httpServer.listen(4200, () => {
+    console.log(`Node SSR server listening on http://localhost:4200`);
+  });
+}