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/

src/main.server.ts

@@ -0,0 +1,24 @@
+import { APP_ID } from '@angular/core';
+import { bootstrapApplication, BootstrapContext } from '@angular/platform-browser';
+import { provideServerRendering, withRoutes } from '@angular/ssr';
+
+import { appConfig } from './app/app.config';
+import { App } from './app/app';
+import { serverRoutes } from './app/app.server.routes';
+
+const serverAppConfig = {
+  ...appConfig,
+  providers: [
+    ...appConfig.providers,
+    { provide: APP_ID, useValue: 'server' },
+    provideServerRendering(withRoutes(serverRoutes)),
+  ],
+};
+
+/**
+ * Bootstrap function for server-side rendering.
+ * Exports a function that accepts BootstrapContext and returns ApplicationRef,
+ * as required by @angular/ssr's CommonEngine bootstrap signature.
+ */
+export default (ctx: BootstrapContext) =>
+  bootstrapApplication(App, serverAppConfig, ctx);