Add interface preview and fix WebView bridge exposure

SUB Control/web_ui.py

@@ -35,7 +35,9 @@ class ControlApi:
         self.motor_directions: dict[int, int] = {}
         self.battery_path = Path(__file__).resolve().parent / "battery_settings.json"
         self.model_path = Path(__file__).resolve().parent / "model_settings.json"
-        self.window = None
+        # Leading underscore keeps the native WebView object out of js_api
+        # serialization. Only the small public methods below are exposed.
+        self._window = None
         self.maximized = False
         self.battery_config = {
             "cells": 4, "capacity_mah": 5500, "c_rating": 35,
@@ -58,29 +60,29 @@ class ControlApi:
         return [p.device for p in list_ports.comports()]
 
     def minimize_window(self):
-        if self.window:
-            self.window.minimize()
+        if self._window:
+            self._window.minimize()
         return True
 
     def toggle_maximize_window(self):
-        if not self.window:
+        if not self._window:
             return False
         if self.maximized:
-            self.window.restore()
+            self._window.restore()
         else:
-            self.window.maximize()
+            self._window.maximize()
         self.maximized = not self.maximized
         return self.maximized
 
     def close_window(self):
-        if self.window:
-            self.window.destroy()
+        if self._window:
+            self._window.destroy()
         return True
 
     def choose_model(self):
-        if not self.window:
+        if not self._window:
             raise RuntimeError("Window is not ready")
-        selected = self.window.create_file_dialog(
+        selected = self._window.create_file_dialog(
             webview.OPEN_DIALOG,
             allow_multiple=False,
             file_types=("STL mesh (*.stl)", "STEP model (*.step;*.stp)"),
@@ -285,7 +287,7 @@ def main():
         background_color="#111719", frameless=True, easy_drag=False,
         shadow=True,
     )
-    api.window = window
+    api._window = window
     window.events.maximized += lambda: setattr(api, "maximized", True)
     window.events.restored += lambda: setattr(api, "maximized", False)
     try: