[FEATURE] Track full deprecation of .claude/commands/ in favor of skills

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Skills (.claude/skills/) are the recommended replacement for commands (.claude/commands/), and many projects have already migrated. However, there's no public timeline or tracking issue for when .claude/commands/ will be fully deprecated and the directory will stop being recognized by Claude Code.

Projects that have migrated need to know when it's safe to remove any backward-compatibility shims, and projects that haven't migrated need to know the deadline.

Proposed Solution

Publish a deprecation timeline for .claude/commands/:

1. When will Claude Code stop reading .claude/commands/ files?
2. Will there be a deprecation warning phase first (e.g., commands still work but show a warning suggesting migration to skills)?
3. Will there be a migration tool or guide for users who haven't migrated yet?

Even if the timeline is "no plans to remove commands soon," having that stated explicitly in an issue would be helpful for project planning.