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/app/structured-data/structured-data.component.ts

@@ -1,4 +1,5 @@
-import { Component, effect, inject } from '@angular/core';
+import { Component, effect, inject, PLATFORM_ID, OnDestroy } from '@angular/core';
+import { isPlatformBrowser } from '@angular/common';
 import { StructuredDataService } from '../services/structured-data.service';
 
 /**
@@ -16,10 +17,14 @@ import { StructuredDataService } from '../services/structured-data.service';
   standalone: true,
   template: '', // renders nothing in the body — writes to <head>
 })
-export class StructuredDataComponent {
+export class StructuredDataComponent implements OnDestroy {
   private service = inject(StructuredDataService);
+  private platformId = inject(PLATFORM_ID);
 
   constructor() {
+    // Only manipulate DOM in the browser; skip on the server.
+    if (!isPlatformBrowser(this.platformId)) return;
+
     effect(() => {
       const entries = this.service.structuredData();
       this.renderEntries(entries);
@@ -27,6 +32,7 @@ export class StructuredDataComponent {
   }
 
   ngOnDestroy(): void {
+    if (!isPlatformBrowser(this.platformId)) return;
     this.clearTags();
   }