feat(github): split list_releases and add get_release tool

[blinkagent]

Summary

This PR addresses context overrun issues when using list_releases on repositories with many releases and large changelogs.

Changes

Breaking Change

• Removed include_body_and_assets parameter from list_releases
• list_releases now returns lightweight metadata only (id, name, tag_name, dates, draft/prerelease flags)

New Tool

• Added get_release tool to fetch full details for a single release:
  • Accepts either release_id (number) or tag (string) to identify the release
  • Returns full body (changelog) and all assets
  • Includes html_url for direct linking

Version Bump

• Bumped @blink-sdk/github from 0.0.22 → 0.1.0

Rationale

The previous design allowed fetching bodies and assets for many releases at once, which could result in 500KB+ responses for repos like coder/coder (24 assets per release, ~1KB changelogs). This would blow the context window even on fresh chats.

The new pattern:

1. List releases (lightweight) to find what you need
2. Fetch specific release(s) with get_release when you need the details

Fixes #83