Fix GitHub Pages deployment failing on release tags

The github-pages environment protection rules only allow deployment
from the main branch.  When a release is published, the workflow runs
in the tag ref context (e.g. refs/tags/v0.2.0), which the environment
rejects.

Fix by:
- Adding push trigger on main so deploys run in a branch context
- Pinning checkout to ref: main so release-triggered builds also
  use the branch (not the detached tag)

https://claude.ai/code/session_01MVwVedn97waTs89PBTnhzb

Author: claude

.github/workflows/docs.yml

@@ -1,6 +1,8 @@
 name: Deploy Docs to GitHub Pages
 
 on:
+  push:
+    branches: [main]
   release:
     types: [published]
   workflow_dispatch:
@@ -23,6 +25,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: main
 
       - name: Set up Python
         uses: actions/setup-python@v5