feat: add mixed package docs access

[jlitola]

Summary

• add first-class mixed package docs access across CLI and MCP with docs list / docs read plus list_package_docs / read_package_doc
• surface explicit doc follow-up metadata from unified search, including alternate read_file fallbacks for repo-backed docs
• tighten gated command/tool registration, docs-specific request/response builders, and protocol guards so docs flows are explicit and agent-friendly

Testing

• bun run typecheck
• bun test
• bun run build
• production smoke checks for docs list, docs read, root help, and docs search flows

Notes

• hosted-doc package version attribution was removed after backend fixes; crawled docs now render truthful unscoped context instead of misleading package versions