Add PyPI Trusted Publishing workflow (OIDC, no stored token)

Author: JonathanSolvesProblems

.github/workflows/publish.yml

@@ -0,0 +1,27 @@
+name: Publish to PyPI
+
+# Publishes coldpath to PyPI via Trusted Publishing (OIDC) -- no API token, no stored secret.
+# Runs when a GitHub release is published, or on demand. Requires a one-time "trusted publisher"
+# entry on PyPI (owner: JonathanSolvesProblems, repo: coldpath, workflow: publish.yml).
+
+on:
+  release:
+    types: [published]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    permissions:
+      id-token: write        # required for Trusted Publishing
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - run: pip install build
+      - run: python -m build
+      - uses: pypa/gh-action-pypi-publish@release/v1