Add trusted publishing workflow for PyPI

Publishes to PyPI via OIDC trusted publishing whenever a GitHub
release is created. No API tokens needed — uses pypa/gh-action-pypi-publish
with the 'pypi' environment for approval gating.

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

Author: keon

.github/workflows/publish.yml

@@ -0,0 +1,44 @@
+name: Publish to PyPI
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install build tools
+        run: python -m pip install --upgrade pip build
+
+      - name: Build package
+        run: python -m build
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: dist
+          path: dist/
+
+  publish:
+    needs: build
+    runs-on: ubuntu-latest
+    environment: pypi
+    permissions:
+      id-token: write
+    steps:
+      - name: Download build artifacts
+        uses: actions/download-artifact@v4
+        with:
+          name: dist
+          path: dist/
+
+      - name: Publish to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1