Deploy docs with GitHub Pages workflow

[Zehina]

Summary

• add a dedicated GitHub Pages workflow that builds MkDocs and deploys on pushes to master
• stop using the old release-only mkdocs gh-deploy path, which no longer matches the current Pages setup
• update the docs site_url to the canonical GitHub Pages URL

Verification

• uv run mkdocs build --strict

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Trigger Pages deploy from the active default branch

This workflow only runs on pushes to master, but in this repository the active branch is main (the checkout has no master ref, and other project metadata like README.md badges and mkdocs.yml edit links target main), so normal doc updates will never trigger a Pages deployment. Since this commit also removed the release-based mkdocs gh-deploy path, this branch filter can silently stop documentation publishing entirely.

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