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

src/app/app.spec.ts

@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+
+describe('App', () => {
+  describe('computed hasStream', () => {
+    it('should return false when stream_url is missing', () => {
+      const streamUrl = '';
+      expect(!!streamUrl && streamUrl.trim().length > 0).toBe(false);
+    });
+
+    it('should return false when stream_url is whitespace', () => {
+      const streamUrl = '   ';
+      expect(!!streamUrl && streamUrl.trim().length > 0).toBe(false);
+    });
+
+    it('should return true when stream_url is a valid URL', () => {
+      const streamUrl = 'https://stream.example.com/live';
+      expect(!!streamUrl && streamUrl.trim().length > 0).toBe(true);
+    });
+  });
+
+  describe('stationConfig title formatting', () => {
+    it('should concatenate name_primary and name_secondary with a space', () => {
+      const namePrimary = 'KM';
+      const nameSecondary = 'TN';
+      const fullName = `${namePrimary} ${nameSecondary}`.trim();
+      expect(fullName).toBe('KM TN');
+    });
+
+    it('should trim trailing space when name_secondary is empty', () => {
+      const namePrimary = 'KM';
+      const nameSecondary = '';
+      const fullName = `${namePrimary} ${nameSecondary}`.trim();
+      expect(fullName).toBe('KM');
+    });
+  });
+});