ci: add Gitea Actions workflow and unit tests

- Add .gitea/workflows/ci.yml: runs build + tests on push/PR to main
- Add vitest as dev dependency
- Add src/utils.test.ts: 4 tests covering handleTool success, Error throw,
  non-Error throw, and arg passthrough
- Add src/client.test.ts: 12 tests covering URL building, Authorization header,
  query string params, Content-Type presence/absence, error handling with
  message extraction and statusText fallback, and HTTP method correctness

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -11,6 +11,7 @@
     "build": "tsc",
     "dev": "tsc --watch",
     "start": "node dist/index.js",
+    "test": "vitest run",
     "prepublishOnly": "pnpm build"
   },
   "dependencies": {
@@ -19,7 +20,8 @@
   },
   "devDependencies": {
     "@types/node": "^22.19.21",
-    "typescript": "^5.9.3"
+    "typescript": "^5.9.3",
+    "vitest": "^4.1.9"
   },
   "engines": {
     "node": ">=22"