Suggested Labels [GA]

### Value Prop
The label picker now surfaces your most relevant labels at the top, so you can apply the right label in seconds instead of scrolling through hundreds of options. A "Suggested labels" group shows labels you've recently used alongside the most popular ones in the repo, each with a short reason so you always know why they appear. This makes labeling faster and more accurate, whether you're triaging a single issue or working through a backlog.

### Expected Outcome
Developers and maintainers spend less time hunting for the right label and more time doing meaningful work, resulting in better-labeled issues and pull requests across the board. By reducing choice fatigue in repos with large label sets, teams can triage more consistently and keep their workflows moving. Over time, smarter label suggestions help contributors get onboarded faster and keep project organization healthy with less manual effort.

The roadmap issue names no repository files, tests, or implementation entry point. Start with the Value Prop and Expected Outcome as product requirements; the work is done when suggested labels surface recently used and popular labels with reasons and reduce label-search effort.

索引モデルが issue の本文から書いたものです。