feat: Add developer-utilities plugin

[adamkwhite]

Summary

This PR adds a new developer-utilities plugin that provides 8 essential commands plus a standalone session picker utility, addressing community-requested features.

Commands Added

1. /clean - Cache and log cleanup (frees 3-6GB typically)
2. /validate-commands - Slash command validation
3. /permission-examples - Permission rule explanation using user's actual settings
4. /init-skills - Skills-aware CLAUDE.md initialization
5. /diagnose-skills - Troubleshoot skill discovery and invocation issues
6. /update-plugins - Update all git-based plugins with one command
7. /list-sessions - List sessions with labels, timestamps, and activity
8. /label-session - Add/update custom labels for sessions

Standalone Utilities

claude-resume - Interactive session picker (terminal script, not a slash command)

• Fuzzy search sessions by label, project, or date
• Edit labels inline (Ctrl+E)
• Delete labels (Ctrl+D)
• Auto-retry on failed resume
• Uses labels created with /label-session

GitHub Issues Addressed

• #11646 - Cache cleanup functionality
• #11655 - Permission rule precedence documentation
• #11632 - Command validation (validation only, reload requires CLI changes)
• #11661 - Skills-first initialization approach
• #11459 - Skills being interpreted as slash commands
• #9716 - Skills not being discovered
• #11322 - Prettier formatting breaks skills
• #11676 - Plugin update-all command
• #3605 - Session renaming/labeling feature request

Plugin Structure

Follows the standard plugin structure used by other official plugins:

• .claude-plugin/plugin.json - Plugin metadata
• commands/*.md - 8 command files
• scripts/claude-resume - Standalone session picker script
• README.md - Comprehensive documentation with installation methods

Session Management Architecture

The session management features use a shared labels file approach:

• /list-sessions and /label-session (slash commands) write to ~/.claude/session-labels.json
• claude-resume (standalone script) reads from the same file
• Non-destructive workaround since Claude Code's internal session DB cannot be safely modified
• Labels persist across sessions and are portable

Testing

All commands have been tested locally:

• All bash commands are single-line (no multi-line if/for/while)
• No command substitution ($()) that breaks in Claude Code
• Commands work in both project and global installations
• /update-plugins successfully tested with git-based plugin
• Session commands tested with label creation, editing, and deletion
• claude-resume tested with fzf interactive features

Installation Methods Documented

1. Plugin Marketplace (recommended)
2. From GitHub Repository (curl)
3. Clone Repository (for development)
4. Local Marketplace (for testing)

Additional: claude-resume script requires fzf and is symlinked to ~/bin/

🤖 Generated with Claude Code