Update banner should show the new version (and ideally a one-line summary)

Currently the update banner reads only:

Update available! Run: winget upgrade Anthropic.ClaudeCode

A user can't tell:

1. What the new version is.
2. Whether it's substantial or a no-op (e.g. 2.1.159 was "Internal infrastructure improvements (no user-facing changes)").
3. Whether the suggested command will even succeed — winget upgrade returns "No applicable upgrade found" for a day or two after each release because the winget catalog lags Anthropic's CDN.

Real example from today (2026-05-31): running 2.1.158 with the banner showing, but winget upgrade Anthropic.ClaudeCode returned No applicable upgrade found because winget hadn't picked up 2.1.159 yet. Confirming this required:

• Checking installed version via claude --version and the on-disk binary (both 2.1.158).
• winget source update + winget show Anthropic.ClaudeCode (still 2.1.158 — winget catalog lag).
• Manually fetching the upstream CHANGELOG.md to discover 2.1.159 existed and that it had no user-facing changes anyway.

Suggestion:

• Show <current> -> <new> (e.g. 2.1.158 -> 2.1.159) and the top changelog line in the banner so users can immediately judge whether to act.
• If the recommended install channel doesn't yet have the new version (winget catalog lag), say so explicitly or point to the direct installer URL on the Anthropic CDN.

Environment: Windows 11, winget-installed Claude Code, running 2.1.158.