Add GitHub Actions workflow to publish to crates.io

Triggers on GitHub release creation. Runs tests then publishes
using the CARGO_REGISTRY_TOKEN secret.

https://claude.ai/code/session_019tzejYnzWFARWNgHBZ4fhN

Author: claude

.github/workflows/publish.yml

@@ -0,0 +1,22 @@
+name: Publish to crates.io
+
+on:
+  release:
+    types: [published]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: dtolnay/rust-toolchain@stable
+
+      - run: cargo test
+
+      - run: cargo publish
+        env:
+          CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}