Show release notes after hunk update

Problem

After hunk update succeeds, the command confirms the installed version but does not provide a direct path to learn what changed.

Proposed behavior

Print a clickable plain URL to the exact release notes after a successful update, and potentially when Hunk is already current.

Interactive example:

◇  Updated to 0.21.0
●  Release notes  https://hunk.dev/changelog/0.21/#v0-21-0
│
└  Done

Plain-output example:

Updated hunk to 0.21.0.
Release notes: https://hunk.dev/changelog/0.21/#v0-21-0

The changelog groups releases by major/minor series and exposes an exact-version anchor, including prerelease anchors such as #v0-21-0-beta-0.

Considerations

• Keep the URL visible and stable in piped/CI output.
• Prefer a plain URL over terminal-only hyperlink escape sequences.
• Decide whether hunk update --check should include the same link for the latest available version.
• Cover stable releases, prereleases, explicit downgrades, and already-current output.