Add GitHub Pages publishing for CogMap

[ryannadel]

CogMap already produces a self-contained HTML artifact, but sharing it required manual branch setup and Pages configuration. This adds a first-class GitHub Pages publishing path so the build skill can refresh a map and publish a shareable URL in the same workflow.

Summary

• Adds publish_github_pages.py, a deterministic publisher that copies the rendered CogMap output to index.html on a Pages branch, includes the data JSON and manifest, pushes the branch, and configures Pages with gh when available.
• Wires refresh.py --publish-github-pages plus publish options for remote, branch, path, dry-run/no-push, and skipping Pages API configuration.
• Documents the publishing flow in the skill and project READMEs, then syncs the .agents skill mirror.
• Adds tests for GitHub remote parsing, Pages URL generation, and local no-push branch payload creation.

Validation

• python -m compileall -q .
• python -m unittest discover -s tests -v
• python cogmap-app/tools/sync_skill.py --check