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/

package.json

@@ -14,14 +14,16 @@
   "private": true,
   "packageManager": "npm@11.11.0",
   "dependencies": {
+    "@angular/cdk": "^21.2.0",
     "@angular/common": "^21.2.0",
     "@angular/compiler": "^21.2.0",
     "@angular/core": "^21.2.0",
     "@angular/forms": "^21.2.0",
     "@angular/platform-browser": "^21.2.0",
+    "@angular/platform-server": "^21.2.19",
     "@angular/router": "^21.2.0",
+    "@angular/ssr": "^21.2.20",
     "@types/leaflet": "^1.9.17",
-    "@angular/cdk": "^21.2.0",
     "chart.js": "^4.4.0",
     "leaflet": "^1.9.4",
     "ng2-charts": "^10.0.0",
@@ -34,11 +36,12 @@
     "@angular/build": "^21.2.14",
     "@angular/cli": "^21.2.14",
     "@angular/compiler-cli": "^21.2.0",
+    "@types/jsdom": "^21.1.7",
+    "@types/node": "^26.1.2",
     "@vitest/coverage-v8": "^4.0.8",
     "jsdom": "^26.1.0",
     "prettier": "^3.8.1",
     "typescript": "~5.9.2",
-    "vitest": "^4.0.8",
-    "@types/jsdom": "^21.1.7"
+    "vitest": "^4.0.8"
   }
 }