ci: add PyPI trusted-publish workflow, manual docs dispatch

Adds .github/workflows/publish.yml: on a published GitHub Release,
build sdist+wheel from the release tag, check metadata with twine,
and publish to PyPI via pypa/gh-action-pypi-publish using OIDC trusted
publishing (permissions: id-token: write) -- no stored token/secret.
Scoped to a "pypi" GitHub Environment so PyPI's trusted-publisher
check is exact (repo + workflow + environment) and so manual-approval
gating can be added later if wanted.

Requires a one-time manual step on PyPI: add a trusted publisher on
the existing pgraph-python project (Settings -> Publishing) naming
this repo, workflow filename, and the "pypi" environment.

Also adds workflow_dispatch to ci.yml's triggers, and widens the docs
job's condition to run on manual dispatch as well as push, so the
Sphinx docs can be manually rebuilt/redeployed on demand without any
relationship to a PyPI release -- the two are on separate triggers
entirely (push+dispatch for docs, release-published only for PyPI).

Verified: pyproject.toml/publish.yml YAML parses; `python -m build`
produces a clean sdist+wheel from this checkout; `twine check` passes
on both; a genuinely isolated venv (confirmed via sys.prefix) installs
the built wheel and successfully imports and exercises real
functionality (UGraph/add_vertex/add_edge/__str__).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: petercorke

.github/workflows/ci.yml

@@ -5,6 +5,7 @@ on:
     branches: [main]
   pull_request:
     branches: [main]
+  workflow_dispatch:
 
 jobs:
   unittest:
@@ -81,7 +82,7 @@ jobs:
           verbose: true
 
   docs:
-    if: github.event_name == 'push'
+    if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
     needs: unittest
     runs-on: ubuntu-latest
     steps:

.github/workflows/publish.yml

@@ -0,0 +1,45 @@
+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: "3.12"
+      - name: Install build tooling
+        run: |
+          python -m pip install --upgrade pip
+          pip install build twine
+      - name: Build sdist and wheel
+        run: python -m build
+      - name: Check metadata
+        run: twine check dist/*
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: dist
+          path: dist/
+
+  publish:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: pypi
+      url: https://pypi.org/project/pgraph-python/
+    permissions:
+      id-token: write  # required for PyPI trusted publishing (OIDC)
+    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