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>

tests/setup/global-setup.ts

@@ -0,0 +1,26 @@
+import { beforeEach, afterEach, vi } from 'vitest';
+
+// Reset mocks between tests
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+// Clean up after each test
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+// Global test timeout
+vi.setConfig({ testTimeout: 10000 });
+
+// Silence console during tests unless DEBUG=true
+if (process.env.DEBUG !== 'true') {
+  global.console = {
+    ...console,
+    log: vi.fn(),
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+  };
+}