feat: support RubyGems and Go registries

[jlitola]

Summary

• Add RubyGems and Go to the shared registry taxonomy used by CLI parsing and MCP package targets.
• Expose the new registries across package info, dependencies, changelog, docs listing, code navigation help, and implementation docs.
• Extend dependency registry gating/tests and keep vulnerability support limited to npm, PyPI, Hex, and Crates.

Verification

• bun test
• bun run typecheck
• bun run lint
• bun run format:check
• bun run build
• bun run smoke:cli
• bun run smoke:mcp
• Live production CLI + MCP-equivalent checks for rubygems:rails and go:golang.org/x/text on pkg info and pkg deps

Notes

• Go dependency version resolution returned different resolved versions for golang.org/x/mod across repeated live calls; backend follow-up is being tracked separately.