test(web): add Vitest setup and unit tests for validations and utils

- Add vitest config and test script to web app
- Auth validation tests: phone format, password rules, registration flow
- Listing validation tests: all schema steps, constants, merged schema
- Utils tests: cn() class merging with Tailwind conflict resolution
- 36 tests across 3 test files

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/vitest.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vitest/config';
+import path from 'path';
+
+export default defineConfig({
+  test: {
+    include: ['**/__tests__/**/*.spec.ts', '**/__tests__/**/*.test.ts'],
+  },
+  resolve: {
+    alias: {
+      '@': path.resolve(__dirname, '.'),
+    },
+  },
+});