feat(09-01): configure Vitest with multi-project setup

- Install Vitest, @vitest/browser, vitest-browser-svelte, @vitest/coverage-v8
- Configure multi-project: client (browser/Playwright) and server (node)
- Add test scripts: test, test:unit, test:unit:watch, test:coverage
- Coverage provider: v8 with autoUpdate thresholds

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -14,6 +14,10 @@
 		"db:migrate": "drizzle-kit migrate",
 		"db:push": "drizzle-kit push",
 		"db:studio": "drizzle-kit studio",
+		"test": "vitest",
+		"test:unit": "vitest run",
+		"test:unit:watch": "vitest",
+		"test:coverage": "vitest run --coverage",
 		"test:e2e": "playwright test",
 		"test:e2e:docker": "BASE_URL=http://localhost:3000 playwright test tests/docker-deployment.spec.ts"
 	},
@@ -24,6 +28,9 @@
 		"@sveltejs/kit": "^2.50.1",
 		"@sveltejs/vite-plugin-svelte": "^6.2.4",
 		"@types/better-sqlite3": "^7.6.13",
+		"@vitest/browser": "^4.0.18",
+		"@vitest/browser-playwright": "^4.0.18",
+		"@vitest/coverage-v8": "^4.0.18",
 		"drizzle-kit": "^0.31.8",
 		"eslint": "^9.39.2",
 		"eslint-config-prettier": "^10.1.8",
@@ -32,7 +39,9 @@
 		"svelte": "^5.48.2",
 		"svelte-check": "^4.3.5",
 		"typescript": "^5.9.3",
-		"vite": "^7.3.1"
+		"vite": "^7.3.1",
+		"vitest": "^4.0.18",
+		"vitest-browser-svelte": "^2.0.2"
 	},
 	"dependencies": {
 		"@tailwindcss/vite": "^4.1.18",