feat: migrate config beside executable

internal/ui/shell.go

@@ -476,6 +476,12 @@ func (s *Shell) SetSettings(value SettingsState) {
 	s.closeOnExit.Value = value.CloseOnExit
 }
 
+// ReportStartupIssue records a safe, user-recoverable configuration message.
+// The application calls it before the frame loop starts; it performs no I/O.
+func (s *Shell) ReportStartupIssue(message string) {
+	s.instanceFeedback = strings.TrimSpace(message)
+}
+
 func (s *Shell) OnSave(fn func(SettingsState)) { s.onSave = fn }
 
 func (s *Shell) OnInstancesChanged(fn func([]InstanceRow)) { s.onInstancesChanged = fn }