docs: update documentation for CLI consolidation (bd-bxqv)

Update docs to reflect CLI command restructuring:
- migrate-tombstones → migrate tombstones
- bd quickstart is now hidden, point to docs/QUICKSTART.md
- Add CLI consolidation section to CHANGELOG.md
- Remove quickstart from command tables

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

skills/beads/SKILL.md

@@ -441,7 +441,6 @@ Shows:
 | `bd workflow` | Show workflow guide | "How do I use beads?" |
 | **ADVANCED COMMANDS** | | |
 | `bd prime` | Refresh AI context | "Load bd workflow rules" |
-| `bd quickstart` | Interactive tutorial | "Teach me beads basics" |
 | `bd daemons` | Multi-repo daemon mgmt | "Manage all beads daemons" |
 | `bd version` | Version check | "Check bd version" |
 | `bd restore <id>` | Restore compacted issue | "Get full history from git" |