feat(renderer): platform-gated dual renderer backend with isolated QtWebEngine profiles

Windows prefers WebView2, Linux uses QtWebEngine only; pythonnet deps are win32-marked. Each QtWebEngine instance gets its own profile under data/webengine, and Chromium flags are sanitized before QApplication (--no-sandbox accepted only for explicit root/container use).

ui/views/custom_web_page.py

@@ -1,4 +1,4 @@
-from PyQt6.QtWebEngineCore import QWebEnginePage, QWebEngineScript
+from PyQt6.QtWebEngineCore import QWebEnginePage, QWebEngineScript, QWebEngineProfile
 from PyQt6.QtCore import QUrl
 from PyQt6.QtGui import QDesktopServices
 
@@ -10,8 +10,19 @@ class CustomWebPage(QWebEnginePage):
     2. 禁用 Ctrl/Meta + 滚轮 及 Ctrl + +/-/0 快捷键的页面缩放
        （浏览器式缩放对桌面聊天工具无意义且易误触）。
     """
-    def __init__(self, parent=None):
-        super().__init__(parent)
+    def __init__(self, profile_or_parent=None, parent=None):
+        # P1-03：兼容两种调用 —— 新式 CustomWebPage(profile, parent) 与旧式 CustomWebPage(parent)。
+        # profile 缺省 None → QtWebEngine 默认 profile；main_window 传入本实例独立 profile。
+        if isinstance(profile_or_parent, QWebEngineProfile):
+            profile, par = profile_or_parent, parent
+        else:
+            profile, par = None, profile_or_parent
+            if parent is not None:
+                raise TypeError("CustomWebPage(profile, parent) 或 CustomWebPage(parent)")
+        if profile is not None:
+            super().__init__(profile, par)
+        else:
+            super().__init__(par)
         self._inject_zoom_lock()
 
     def _inject_zoom_lock(self):

ui/views/wv2_view.py

@@ -21,6 +21,7 @@ _BRIDGE_METHODS = (
     "onDeleteMessageClicked",
     "onAttachmentClicked",
     "onScrollChanged",
+    "onRequestWindowPage",  # 🆕 P1-01 渲染窗口换页请求
 )