ci: add GitHub Actions test + typecheck workflow

Runs vitest and tsc --noEmit on Node 20 on push to main and PRs.
Includes package-lock.json for deterministic npm ci installs.

Author: AgentSIM

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    name: Tests + Typecheck (Node 20)
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+          cache: npm
+
+      - run: npm ci
+
+      - run: npm run typecheck
+
+      - run: npm test