fix(crew): add dry-run support and error handling to crew stop (gt-kjcx4)

Fixed two issues in `gt crew stop <name>`:

1. --dry-run flag now works for individual crew stops (previously only
   worked with --all)

2. HasSession errors are now properly handled instead of being ignored,
   which could cause "No session found" messages even when sessions exist

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

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

internal/cmd/crew_lifecycle.go

@@ -666,12 +666,23 @@ func runCrewStop(cmd *cobra.Command, args []string) error {
 		sessionID := crewSessionName(r.Name, name)
 
 		// Check if session exists
-		hasSession, _ := t.HasSession(sessionID)
+		hasSession, err := t.HasSession(sessionID)
+		if err != nil {
+			fmt.Printf("Error checking session %s: %v\n", sessionID, err)
+			lastErr = err
+			continue
+		}
 		if !hasSession {
 			fmt.Printf("No session found for %s/%s\n", r.Name, name)
 			continue
 		}
 
+		// Dry run - just show what would be stopped
+		if crewDryRun {
+			fmt.Printf("Would stop %s/%s (session: %s)\n", r.Name, name, sessionID)
+			continue
+		}
+
 		// Capture output before stopping (best effort)
 		var output string
 		if !crewForce {