fix(mr): show discussion prefixes in note list

Description

Show the existing eight-character discussion prefix for replyable one-note discussions in human-readable glab mr note list output.

Document how to use the copy-safe prefix with glab mr note create --reply, and how to retrieve full IDs from JSON. Preserve both mr view --comments formats and JSON serialization.

Related Issues

Resolves #8284 (closed)

How has this been tested?

• Focused note-list, create-help, renderer, and TTY/raw view tests
• make check in a standalone checkout: 3,929 tests passed, 8 skipped
• make build
• make lint
• make gen-docs idempotency
• pre-push generated checks and 539 changed-package tests