[Copilot]

The window renders a redundant native OS title bar (with its own min/max/close controls) above the in-app header, which already provides a close button. This makes the window borderless and keeps it movable via in-app drag surfaces.

Changes

• Window setup (app.rs): set decorations: false in window::Settings so the native title bar is not rendered.

• Window dragging (app.rs): added a DragWindow message handled via window::drag(id), plus an App::drag() helper returning the message when a window exists. A borderless window has no native drag handle, so dragging must be initiated in-app:

Message::DragWindow => {
    if let Some(id) = self.window_id {
        return window::drag(id);
    }
}

• Drag surfaces:
  • components/header.rs — main header row (title, status badge, settings, ×) wrapped in a mouse_area that starts the drag; child buttons still capture their own presses, so 设置 and × keep working.
  • components/dialog.rs — dialog::header now accepts a drag: Option<Message> applied to the title strip only, excluding the close button so its click isn't swallowed by the drag.
  • views/settings.rs, views/update.rs, components/feedback.rs — pass app.drag() through to their dialog headers (settings, update, and notice dialogs all draggable).

Closing behavior is unchanged: the in-app × button, Esc, and tray menu still close the window to the tray.

• Fixes [UI] Unexcepted title bar / 应该移除的标题栏 #23