Add GitHub Actions CI pipeline

- Lint & typecheck on every push/PR
- Build verification
- Docker build test
- Multi-arch Docker publish to GHCR on main (amd64 + arm64)
- Build cache via GitHub Actions cache
- Concurrency control to cancel stale runs

.github/workflows/ci.yml

@@ -0,0 +1,107 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lint-and-typecheck:
+    name: Lint & Typecheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm typecheck
+
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    needs: lint-and-typecheck
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm build
+
+  docker:
+    name: Docker Build
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: docker/Dockerfile
+          push: false
+          tags: stirling-image:ci
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+  docker-publish:
+    name: Publish Docker Image
+    runs-on: ubuntu-latest
+    needs: docker
+    if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-qemu-action@v3
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - uses: docker/metadata-action@v5
+        id: meta
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            type=sha
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: docker/Dockerfile
+          push: true
+          platforms: linux/amd64,linux/arm64
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max