Extract SupportedShells constant to constants package (gt-4u682)

- Added constants.SupportedShells for consistent shell list
- Updated 7 usages across start.go, crew_lifecycle.go, crew_helpers.go, tmux.go
- All tests pass

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

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

internal/cmd/crew_helpers.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 	"syscall"
 
+	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/crew"
 	"github.com/steveyegge/gastown/internal/git"
 	"github.com/steveyegge/gastown/internal/rig"
@@ -137,7 +138,7 @@ func detectCrewFromCwd() (*crewDetection, error) {
 
 // isShellCommand checks if the command is a shell (meaning Claude has exited).
 func isShellCommand(cmd string) bool {
-	shells := []string{"bash", "zsh", "sh", "fish", "tcsh", "ksh"}
+	shells := constants.SupportedShells
 	for _, shell := range shells {
 		if cmd == shell {
 			return true

internal/cmd/crew_lifecycle.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/crew"
 	"github.com/steveyegge/gastown/internal/mail"
 	"github.com/steveyegge/gastown/internal/style"
@@ -248,7 +249,7 @@ func runCrewRestart(cmd *cobra.Command, args []string) error {
 	}
 
 	// Wait for Claude to start, then prime it
-	shells := []string{"bash", "zsh", "sh", "fish", "tcsh", "ksh"}
+	shells := constants.SupportedShells
 	if err := t.WaitForCommand(sessionID, shells, 15*time.Second); err != nil {
 		style.PrintWarning("Timeout waiting for Claude to start: %v", err)
 	}
@@ -413,7 +414,7 @@ func restartCrewSession(rigName, crewName, clonePath string) error {
 	}
 
 	// Wait for Claude to start, then prime it
-	shells := []string{"bash", "zsh", "sh", "fish", "tcsh", "ksh"}
+	shells := constants.SupportedShells
 	if err := t.WaitForCommand(sessionID, shells, 15*time.Second); err != nil {
 		// Non-fatal warning
 	}