ci: Add crates.io trusted publishing workflow (#58)

Add a GitHub Actions workflow for trusted publishing to crates.io using
OIDC authentication. This enables secure, tokenless publishing when
pushing version tags (v*) to the repository.

Part of bootc-dev/infra#20

Assisted-by: OpenCode (claude-opus-4-5@20251101)

Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

.github/workflows/cratesio-release.yml

@@ -0,0 +1,18 @@
+# See https://crates.io/docs/trusted-publishing
+name: Publish to crates.io
+on:
+  push:
+    tags: ['v*']  # Triggers when pushing tags starting with 'v'
+jobs:
+  publish:
+    runs-on: ubuntu-24.04
+    permissions:
+      id-token: write     # Required for OIDC token exchange
+    steps:
+    - uses: actions/checkout@v6
+    - uses: rust-lang/crates-io-auth-action@v1
+      id: auth
+    - run: cargo publish
+      env:
+        CARGO_REGISTRY_TOKEN: ${{ steps.auth.outputs.token }}
+