Move docs hosting to Read the Docs

[0sparsh2]

Summary

• add Read the Docs configuration via .readthedocs.yaml
• add docs/requirements.txt for MkDocs Material builds on RTD
• remove GitHub Pages workflow so this repo no longer publishes under the personal domain project path
• update docs metadata and package URL to the Read the Docs target

Validation

• .venv/bin/mkdocs build --clean
• confirmed the repository-level GitHub Pages endpoint now returns 404 after disabling Pages

Follow-up

After merge, import the public repo in Read the Docs Community using the slug agentbridge if available; otherwise update site_url and package metadata to the chosen RTD slug.

Closes #82