test: migrate from Jest to Vitest (Phase 1 complete)

- Remove Jest and all related packages
- Install Vitest with coverage support
- Create vitest.config.ts with path aliases
- Set up global test configuration
- Migrate all 6 test files to Vitest syntax
- Update TypeScript configuration for better Vitest support
- Create separate tsconfig.build.json for clean builds
- Fix all import/module issues in tests
- All 68 tests passing successfully
- Current coverage baseline: 2.45%

Phase 1 of testing suite improvement complete.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

vitest.config.ts

@@ -0,0 +1,34 @@
+import { defineConfig } from 'vitest/config';
+import path from 'path';
+
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: 'node',
+    setupFiles: ['./tests/setup/global-setup.ts'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html', 'lcov'],
+      exclude: [
+        'node_modules/',
+        'tests/',
+        '**/*.d.ts',
+        '**/*.test.ts',
+        'scripts/',
+        'dist/'
+      ],
+      thresholds: {
+        lines: 80,
+        functions: 80,
+        branches: 75,
+        statements: 80
+      }
+    }
+  },
+  resolve: {
+    alias: {
+      '@': path.resolve(__dirname, './src'),
+      '@tests': path.resolve(__dirname, './tests')
+    }
+  }
+});