feat(test): add comprehensive test suite and testing infrastructure

- Add vitest configuration with coverage reporting
- Create test setup file with DOM mocks
- Add tests for state management, helpers, and tool configurations
- Update tsconfig and package.json for testing support
- Clean up unused comments and improve code style

package.json

@@ -8,18 +8,28 @@
     "dev": "vite",
     "build": "tsc && vite build",
     "preview": "vite preview",
-    "obfuscate": "node scripts/build.mjs"
+    "obfuscate": "node scripts/build.mjs",
+    "test": "vitest",
+    "test:ui": "vitest --ui",
+    "test:run": "vitest run",
+    "test:coverage": "vitest run --coverage",
+    "test:watch": "vitest watch"
   },
   "devDependencies": {
+    "@testing-library/dom": "^10.4.1",
     "@types/blob-stream": "^0.1.33",
     "@types/html2canvas": "^0.5.35",
     "@types/pdfkit": "^0.17.3",
     "@types/sortablejs": "^1.15.8",
     "@types/utif": "^3.0.6",
+    "@vitest/coverage-v8": "^3.2.4",
+    "@vitest/ui": "^3.2.4",
+    "jsdom": "^27.0.0",
     "ts-migrate": "^0.1.35",
     "typescript": "~5.9.3",
     "vite": "^7.1.7",
-    "vite-plugin-node-polyfills": "^0.24.0"
+    "vite-plugin-node-polyfills": "^0.24.0",
+    "vitest": "^3.2.4"
   },
   "dependencies": {
     "@tailwindcss/vite": "^4.1.14",