refactor: use Vitest projects config instead of deprecated workspace

- Add root vitest.config.ts with projects array (replaces deprecated workspace)
- Add name property to each project's vitest.config.ts for filtering
- Update package.json test scripts to use vitest projects
- Add vitest to root devDependencies

This addresses the Vitest warning about multiple configs impacting
performance by running all projects in a single Vitest process.

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

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

package.json

@@ -42,10 +42,12 @@
     "lint": "npm run lint --workspace=apps/ui",
     "test": "npm run test --workspace=apps/ui",
     "test:headed": "npm run test:headed --workspace=apps/ui",
-    "test:server": "npm run test --workspace=apps/server",
-    "test:server:coverage": "npm run test:cov --workspace=apps/server",
-    "test:packages": "npm run test -w @automaker/types -w @automaker/utils -w @automaker/prompts -w @automaker/platform -w @automaker/model-resolver -w @automaker/dependency-resolver -w @automaker/git-utils --if-present",
-    "test:all": "npm run test:packages && npm run test:server",
+    "test:packages": "vitest run --project=utils --project=platform --project=prompts --project=model-resolver --project=dependency-resolver --project=git-utils",
+    "test:server": "vitest run --project=server",
+    "test:server:coverage": "vitest run --project=server --coverage",
+    "test:unit": "vitest run",
+    "test:unit:watch": "vitest",
+    "test:all": "vitest run",
     "lint:lockfile": "node scripts/lint-lockfile.mjs",
     "format": "prettier --write .",
     "format:check": "prettier --check .",
@@ -64,6 +66,7 @@
   "devDependencies": {
     "husky": "9.1.7",
     "lint-staged": "16.2.7",
-    "prettier": "3.7.4"
+    "prettier": "3.7.4",
+    "vitest": "4.0.16"
   }
 }