fix: don't restart Boot Verify pulse after step 4 already completed it

Step 4's _run_step_4_load_main_program() already marks each sub-step
individually via set_step_complete/set_step_error. But the outer
_run_steps_worker() called set_phase('Boot Verify') on success, which
re-entered the 'running' phase and started a fresh pulse animation
(because _stop_pulse cleared _pulse_job).

Fix: on success, do nothing (sub-steps are already green). Only set
error on failure.

src/gui/main_window.py

@@ -1436,11 +1436,10 @@ class MainWindow(ctk.CTk):
                     else:
                         self._sub_step_frame.set_phase("error")
 
-                # Step 4: mark sub-steps based on result
+                # Step 4: sub-steps already marked individually inside _run_step_4;
+                # avoid set_phase which would restart a pulse on Boot Verify.
                 if i == 3 and hasattr(self, '_tftp_sub_step_frame'):
-                    if success:
-                        self._tftp_sub_step_frame.set_phase("Boot Verify")
-                    else:
+                    if not success:
                         self._tftp_sub_step_frame.set_step_error("Boot Verify")
             except Exception as e:
                 results.append(False)