Publish LocalMath documentation with GitHub Pages

[PraneethMerugu]

Summary

• expand the documentation landing page with installation, an executable example, core vocabulary, guarantees, and guide navigation
• add guarded Documenter deployment and canonical site metadata
• publish main and tag documentation through a dedicated GitHub Actions workflow while retaining read-only pull-request documentation checks

Validation

• full Documenter build, doctests, cross-references, and exported API checks pass locally
• workflow YAML parses successfully
• git diff check passes