chore: Remove unused slash commands

Deleted commands based on usage analysis:
- /help (0 uses) - Claude Code has built-in help
- /utilities (0 uses) - Functions moved to /dev

Remaining commands (9):
- /dev (44 uses) - Development workflow
- /workflows (29 uses) - AI workflows
- /release (23 uses) - Release prep
- /docs (13 uses) - Documentation
- /agent (11 uses) - Agent management
- /testing (7 uses) - Test execution
- /plan (4 uses) - Development planning
- /context (2 uses) - Context management
- /learning (1 use) - Session evaluation

This cleanup reduces command clutter while keeping all actively-used functionality.

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

Author: silversurfer562