🐛 fix: sub-step readability, erase_all workaround, error state

Fix 1 — SubStepFrame readability:
- FONT_BODY (12pt) instead of FONT_SMALL dots/labels
- Number-circle colored dots (CIRCLE_PENDING/RUNNING/COMPLETE/ERROR)
- Accent-colored labels matching StepHeader (ACCENT_*)
- Percentage label next to running phase name

Fix 2 — erase_all full-chip erase:
- Creates temp zero-filled file of flash capacity (from flash_model)
- Uses -erase_only with dummy file instead of failing -erase_all flag
- Supports s25fl256s1 (32MB) which lacks density info for -erase_all
- _flash_capacity() maps model name→bytes

Fix 3 — Error state:
- set_phase('error') shows ✗ red on all sub-steps
- Only shows 'done' (green ●) on actual success

Fix 4 — Style consistency:
- Sub-step colors match StepHeader: CIRCLE_*/ACCENT_*/SUCCESS/DANGER

src/gui/main_window.py

@@ -1055,9 +1055,12 @@ class MainWindow(ctk.CTk):
                 elapsed = time.time() - t_step_start
                 self._log_message(f"  ⏱ Step {i+1} completed in {elapsed:.0f}s")
 
-                # Step 2: mark all sub-steps done
+                # Step 2: mark sub-steps based on result
                 if i == 1 and hasattr(self, '_sub_step_frame'):
-                    self._sub_step_frame.set_phase("done")
+                    if success:
+                        self._sub_step_frame.set_phase("done")
+                    else:
+                        self._sub_step_frame.set_phase("error")
             except Exception as e:
                 results.append(False)
                 self._set_step_status(i, "error")