add project setup

.github/workflows/ci.yml

@@ -0,0 +1,40 @@
+name: CI
+
+on:
+  push:
+    branches: [master, main]
+  pull_request:
+
+jobs:
+  ci:
+    name: Typecheck & Lint (Node ${{ matrix.node-version }})
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [20, 22]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type check
+        run: npm run typecheck
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Format check
+        run: npm run format:check
+
+# Note: The test suite is intentionally excluded from CI.
+# Tests spawn real tmux sessions and require a full system environment.
+# Run tests locally with: npx vitest run test/<file>.test.ts