Add gt start command to boot Gas Town

Starts Deacon and Mayor in the correct order. Other agents
(Witnesses, Refineries, Polecats) start lazily as needed.

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

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

internal/cmd/start.go

@@ -0,0 +1,73 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/tmux"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+var startCmd = &cobra.Command{
+	Use:   "start",
+	Short: "Start Gas Town",
+	Long: `Start Gas Town by launching the Deacon and Mayor.
+
+The Deacon is the health-check orchestrator that monitors Mayor and Witnesses.
+The Mayor is the global coordinator that dispatches work.
+
+Other agents (Witnesses, Refineries, Polecats) are started lazily as needed.
+
+To stop Gas Town, use 'gt deacon stop' and 'gt mayor stop'.`,
+	RunE: runStart,
+}
+
+func init() {
+	rootCmd.AddCommand(startCmd)
+}
+
+func runStart(cmd *cobra.Command, args []string) error {
+	// Verify we're in a Gas Town workspace
+	townRoot, err := workspace.FindFromCwdOrError()
+	if err != nil {
+		return fmt.Errorf("not in a Gas Town workspace: %w", err)
+	}
+
+	t := tmux.NewTmux()
+
+	fmt.Printf("Starting Gas Town from %s\n\n", style.Dim.Render(townRoot))
+
+	// Start Mayor first (so Deacon sees it as up)
+	mayorRunning, _ := t.HasSession(MayorSessionName)
+	if mayorRunning {
+		fmt.Printf("  %s Mayor already running\n", style.Dim.Render("○"))
+	} else {
+		fmt.Printf("  %s Starting Mayor...\n", style.Bold.Render("→"))
+		if err := startMayorSession(t); err != nil {
+			return fmt.Errorf("starting Mayor: %w", err)
+		}
+		fmt.Printf("  %s Mayor started\n", style.Bold.Render("✓"))
+	}
+
+	// Start Deacon (health monitor)
+	deaconRunning, _ := t.HasSession(DeaconSessionName)
+	if deaconRunning {
+		fmt.Printf("  %s Deacon already running\n", style.Dim.Render("○"))
+	} else {
+		fmt.Printf("  %s Starting Deacon...\n", style.Bold.Render("→"))
+		if err := startDeaconSession(t); err != nil {
+			return fmt.Errorf("starting Deacon: %w", err)
+		}
+		fmt.Printf("  %s Deacon started\n", style.Bold.Render("✓"))
+	}
+
+	fmt.Println()
+	fmt.Printf("%s Gas Town is running\n", style.Bold.Render("✓"))
+	fmt.Println()
+	fmt.Printf("  Attach to Mayor:  %s\n", style.Dim.Render("gt mayor attach"))
+	fmt.Printf("  Attach to Deacon: %s\n", style.Dim.Render("gt deacon attach"))
+	fmt.Printf("  Check status:     %s\n", style.Dim.Render("gt status"))
+
+	return nil
+}