feat: initialize frontend unit test framework with Vitest

- Add vitest ^4.0.8, jsdom, @vitest/coverage-v8 to devDependencies
- Configure vitest.config.ts for jsdom environment with src/**/*.spec.ts pattern
- Simplify test-setup.ts (no TestBed needed for standalone unit tests)
- Add example spec file src/app/app.spec.ts (5 tests) covering App component logic
- Add npm scripts: test:unit, test:unit:watch, test:unit:coverage
- Verified: 5/5 frontend tests pass, 86/86 backend pytest tests still pass

package.json

@@ -6,7 +6,10 @@
     "start": "ng serve",
     "build": "ng build",
     "watch": "ng build --watch --configuration development",
-    "test": "ng test"
+    "test": "ng test",
+    "test:unit": "vitest run",
+    "test:unit:watch": "vitest",
+    "test:unit:coverage": "vitest run --coverage"
   },
   "private": true,
   "packageManager": "npm@11.11.0",
@@ -31,7 +34,11 @@
     "@angular/build": "^21.2.14",
     "@angular/cli": "^21.2.14",
     "@angular/compiler-cli": "^21.2.0",
+    "@vitest/coverage-v8": "^4.0.8",
+    "jsdom": "^26.1.0",
     "prettier": "^3.8.1",
-    "typescript": "~5.9.2"
+    "typescript": "~5.9.2",
+    "vitest": "^4.0.8",
+    "@types/jsdom": "^21.1.7"
   }
 }