Add GitHub Actions workflow for release binaries

Builds macOS arm64 and Linux amd64 binaries on tag push
and attaches them to the GitHub release.

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

Author: johnmorrow

.github/workflows/release.yml

@@ -0,0 +1,43 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        include:
+          - os: ubuntu-latest
+            target: x86_64-unknown-linux-gnu
+            artifact: pk-linux-amd64
+          - os: macos-latest
+            target: aarch64-apple-darwin
+            artifact: pk-macos-arm64
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo build --release --target ${{ matrix.target }}
+      - run: cp target/${{ matrix.target }}/release/pk ${{ matrix.artifact }}
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ${{ matrix.artifact }}
+          path: ${{ matrix.artifact }}
+
+  release:
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          merge-multiple: true
+      - run: chmod +x pk-*
+      - uses: softprops/action-gh-release@v2
+        with:
+          files: pk-*