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>

tsconfig.json

@@ -3,8 +3,9 @@
     "target": "ES2020",
     "module": "commonjs",
     "lib": ["ES2020"],
+    "types": ["node", "vitest/globals"],
     "outDir": "./dist",
-    "rootDir": "./src",
+    "rootDir": "./",
     "strict": true,
     "esModuleInterop": true,
     "skipLibCheck": true,
@@ -25,8 +26,14 @@
     "noUnusedParameters": false,
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,
-    "moduleResolution": "node"
+    "moduleResolution": "node",
+    "allowJs": true,
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["src/*"],
+      "@tests/*": ["tests/*"]
+    }
   },
-  "include": ["src/**/*"],
-  "exclude": ["node_modules", "dist", "**/*.test.ts"]
+  "include": ["src/**/*", "tests/**/*", "vitest.config.ts", "types/**/*"],
+  "exclude": ["node_modules", "dist"]
 }