feat(crew): Provision .claude/commands/ for crew and polecat workspaces (gt-jhr85)

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

internal/cmd/doctor.go

@@ -137,6 +137,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 
 	// Crew workspace checks
 	d.Register(doctor.NewCrewStateCheck())
+	d.Register(doctor.NewCommandsCheck())
 
 	// Lifecycle hygiene checks
 	d.Register(doctor.NewLifecycleHygieneCheck())