config: Add Vitest configuration to exclude E2E tests

Vitest was incorrectly running Playwright E2E test files,
causing test suite failures. Added vitest.config.ts to:
- Exclude E2E test folder from unit test runs
- Configure jsdom environment for component testing
- Separate concerns: 'pnpm test' for units, 'pnpm e2e' for E2E

Result: All 176 tests now pass
- Backend: 135/135 (40 unit + 95 integration)
- Frontend: 41/41 (40 unit + 1 E2E)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/vitest.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vitest/config'
+import vue from '@vitejs/plugin-vue'
+import { fileURLToPath, URL } from 'node:url'
+
+export default defineConfig({
+  plugins: [vue()],
+  resolve: { alias: { '@': fileURLToPath(new URL('./src', import.meta.url)) } },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    exclude: ['node_modules', 'dist', 'e2e']
+  }
+})