feat(refinery,boot): add --agent flag for model selection (#469)

* feat(refinery,boot): add --agent flag for model selection (hq-7d5m)

Add --agent flag to gt refinery start/attach/restart and gt boot spawn
commands for consistent model selection across all agent launch points.

Implementation follows the existing pattern from gt deacon start:
- Add StringVar flag for agent alias
- Pass override to Manager/Boot via SetAgentOverride()
- Use BuildAgentStartupCommandWithAgentOverride when override is set

Files affected:
- cmd/gt/refinery.go: add flags to start/attach/restart commands
- internal/refinery/manager.go: add SetAgentOverride and use in Start()
- cmd/gt/boot.go: add flag to spawn command
- internal/boot/boot.go: add SetAgentOverride and use in spawnTmux()

Closes #438

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

* refactor(refinery,boot): use parameter-passing pattern for --agent flag

Address PR review feedback:

1. ADD TESTS: Add tests for --agent flag existence following witness_test.go pattern
   - internal/cmd/refinery_test.go: tests for start/attach/restart
   - internal/cmd/boot_test.go: test for spawn

2. ALIGN PATTERN: Change from setter pattern to parameter-passing pattern
   - Manager.Start(foreground, agentOverride) instead of SetAgentOverride + Start
   - Boot.Spawn(agentOverride) instead of SetAgentOverride + Spawn
   - Matches witness.go style: Start(foreground bool, agentOverride string, ...)

Updated all callers to pass empty string for default agent:
- internal/daemon/daemon.go
- internal/cmd/rig.go
- internal/cmd/start.go
- internal/cmd/up.go

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

---------

Co-authored-by: furiosa <will@saults.io>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/refinery.go

@@ -16,9 +16,10 @@ import (
 
 // Refinery command flags
 var (
-	refineryForeground bool
-	refineryStatusJSON bool
-	refineryQueueJSON  bool
+	refineryForeground    bool
+	refineryStatusJSON    bool
+	refineryQueueJSON     bool
+	refineryAgentOverride string
 )
 
 var refineryCmd = &cobra.Command{
@@ -208,6 +209,13 @@ var refineryBlockedJSON bool
 func init() {
 	// Start flags
 	refineryStartCmd.Flags().BoolVar(&refineryForeground, "foreground", false, "Run in foreground (default: background)")
+	refineryStartCmd.Flags().StringVar(&refineryAgentOverride, "agent", "", "Agent alias to run the Refinery with (overrides town default)")
+
+	// Attach flags
+	refineryAttachCmd.Flags().StringVar(&refineryAgentOverride, "agent", "", "Agent alias to run the Refinery with (overrides town default)")
+
+	// Restart flags
+	refineryRestartCmd.Flags().StringVar(&refineryAgentOverride, "agent", "", "Agent alias to run the Refinery with (overrides town default)")
 
 	// Status flags
 	refineryStatusCmd.Flags().BoolVar(&refineryStatusJSON, "json", false, "Output as JSON")
@@ -277,7 +285,7 @@ func runRefineryStart(cmd *cobra.Command, args []string) error {
 
 	fmt.Printf("Starting refinery for %s...\n", rigName)
 
-	if err := mgr.Start(refineryForeground); err != nil {
+	if err := mgr.Start(refineryForeground, refineryAgentOverride); err != nil {
 		if err == refinery.ErrAlreadyRunning {
 			fmt.Printf("%s Refinery is already running\n", style.Dim.Render("⚠"))
 			return nil
@@ -490,7 +498,7 @@ func runRefineryAttach(cmd *cobra.Command, args []string) error {
 	if !running {
 		// Auto-start if not running
 		fmt.Printf("Refinery not running for %s, starting...\n", rigName)
-		if err := mgr.Start(false); err != nil {
+		if err := mgr.Start(false, refineryAgentOverride); err != nil {
 			return fmt.Errorf("starting refinery: %w", err)
 		}
 		fmt.Printf("%s Refinery started\n", style.Bold.Render("✓"))
@@ -519,7 +527,7 @@ func runRefineryRestart(cmd *cobra.Command, args []string) error {
 	}
 
 	// Start fresh
-	if err := mgr.Start(false); err != nil {
+	if err := mgr.Start(false, refineryAgentOverride); err != nil {
 		return fmt.Errorf("starting refinery: %w", err)
 	}