Add generic Hermes GitHub App plugin

[JWhitleyWork]

Summary

• Add a generic Hermes GitHub App plugin with per-agent GitHub App auth
• Register Hermes tools for REST/GraphQL/issues/PR operations and bundled github-app-workflow skill
• Add hermes-github-app setup and doctor commands plus gh-app/git-app wrappers for token-backed CLI/git flows
• Use GitHub App client_id for JWT issuer and GitHub App installation scope for repository access control
• Include package metadata, CI, tests, docs, and generic branding

Verification

• ruff format .
• ruff check .
• mypy
• pytest
• python -m build
• hermes-github-app setup --help
• non-interactive setup smoke test with temp HERMES_HOME
• hermes-github-app doctor --skip-network
• verified removed local allowlist feature references are absent