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

package.json

@@ -5,11 +5,14 @@
     "ng": "ng",
     "start": "ng serve",
     "build": "ng build",
+    "build:ssr": "ng build",
+    "build:prerender": "ng build",
     "watch": "ng build --watch --configuration development",
     "test": "ng test",
     "test:unit": "vitest run",
     "test:unit:watch": "vitest",
-    "test:unit:coverage": "vitest run --coverage"
+    "test:unit:coverage": "vitest run --coverage",
+    "serve:ssr:radio-station": "node dist/radio-station/server/server.mjs"
   },
   "private": true,
   "packageManager": "npm@11.11.0",