🐛 fix: sub-step default expanded, real-time checkbox, startup freeze, color sync

1. SubStepFrame defaults to expanded (▼), not collapsed
2. erase_all checkbox has command=_on_erase_toggle → immediate config update
3. _deferred_init runs _check_vitis/_refresh_ports in background thread
   Fixes UI freeze during startup (subprocess.run for tool versions)
4. Sub-step colors now match StepHeader:
   - pending: gray ACCENT_PENDING (#888888)
   - running: blue CIRCLE_RUNNING (#0078D4) with pulse animation
   - complete: green ACCENT_COMPLETE (#107C10)
   - error: red ACCENT_ERROR (#D13438)
   - Running sub-step pulses between light/dark blue like StepHeader

src/gui/main_window.py

@@ -97,9 +97,11 @@ class MainWindow(ctk.CTk):
         self.after(100, self._deferred_init)
 
     def _deferred_init(self) -> None:
-        """Run blocking operations after the window is shown."""
-        self._check_vitis()
-        self._refresh_ports_initial()
+        """Run blocking operations in background thread after window shown."""
+        def _bg_init():
+            self._check_vitis()
+            self._refresh_ports_initial()
+        threading.Thread(target=_bg_init, daemon=True).start()
 
     # ── Config ─────────────────────────────────────────────────
 
@@ -212,6 +214,11 @@ class MainWindow(ctk.CTk):
             self._log_message(f"  ✗ Save failed: {e}")
             self._status.set_status(f"Save failed: {e}", "error")
 
+    def _on_erase_toggle(self) -> None:
+        """Update config.erase_all immediately when checkbox toggles."""
+        if self._config:
+            self._config.erase_all = self._erase_cb_var.get()
+
     # ── UI Construction ────────────────────────────────────────
 
     def _build_ui(self) -> None:
@@ -485,6 +492,7 @@ class MainWindow(ctk.CTk):
             text="整片Flash擦除 (Erase entire flash)",
             variable=self._erase_cb_var,
             font=FONT_SMALL,
+            command=self._on_erase_toggle,
         )
         self._erase_cb.grid(row=0, column=0, sticky="w", padx=PADDING_SMALL)