When adding a crew member with 'gt crew add' or spawning a polecat,
provision the .claude/commands/ directory with standard slash commands
like /handoff. This ensures all agents have Gas Town utilities even if
the source repo does not have them tracked.
Changes:
- Add embedded commands templates (internal/templates/commands/)
- Add ProvisionCommands() to templates package
- Call ProvisionCommands from crew and polecat managers
- Add gt doctor commands-provisioned check with --fix support
