Add CI and release workflows

- CI: build + smoke test on push/PR (ubuntu + macos)
- Release: cross-compile on tag push, attach tarballs + sha256 to
  GitHub release (linux x86_64/aarch64, darwin x86_64/aarch64)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: fielding

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: mlugg/setup-zig@v2
+        with:
+          version: 0.15.2
+
+      - name: Install libgit2 (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y libgit2-dev
+
+      - name: Install libgit2 (macOS)
+        if: runner.os == 'macOS'
+        run: brew install libgit2
+
+      - name: Build
+        run: zig build
+
+      - name: Build (ReleaseFast)
+        run: zig build -Doptimize=ReleaseFast
+
+      - name: Smoke test
+        run: |
+          git log --oneline -5
+          ./zig-out/bin/nit status
+          ./zig-out/bin/nit log -n 5
+          ./zig-out/bin/nit show

.github/workflows/release.yml

@@ -0,0 +1,77 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        include:
+          - os: ubuntu-latest
+            target: x86_64-linux
+            name: nit-linux-x86_64
+          - os: ubuntu-latest
+            target: aarch64-linux
+            name: nit-linux-aarch64
+          - os: macos-latest
+            target: x86_64-macos
+            name: nit-darwin-x86_64
+          - os: macos-latest
+            target: aarch64-macos
+            name: nit-darwin-aarch64
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: mlugg/setup-zig@v2
+        with:
+          version: 0.15.2
+
+      - name: Install libgit2 (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y libgit2-dev
+
+      - name: Install libgit2 (macOS)
+        if: runner.os == 'macOS'
+        run: brew install libgit2
+
+      - name: Build
+        run: zig build -Doptimize=ReleaseFast
+
+      - name: Package
+        run: |
+          cp zig-out/bin/nit nit
+          tar czf ${{ matrix.name }}.tar.gz nit
+          shasum -a 256 ${{ matrix.name }}.tar.gz > ${{ matrix.name }}.tar.gz.sha256
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: ${{ matrix.name }}
+          path: |
+            ${{ matrix.name }}.tar.gz
+            ${{ matrix.name }}.tar.gz.sha256
+
+  release:
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          merge-multiple: true
+
+      - name: Create release
+        uses: softprops/action-gh-release@v2
+        with:
+          generate_release_notes: true
+          files: |
+            *.tar.gz
+            *.sha256