Plug three holes in Servo input forwarding

1. Scroll no longer wipes keyboard focus. Servo holds DOM focus across
   wheel events; the shell was clearing keyboard_focus and typed_texts
   on every scroll, so a focused input went deaf the moment the user
   scrolled. Scroll still drops the buffered click point because that
   coordinate is captured against the pre-scroll viewport.

2. Mouse-down hands focus to the shell's root focus handle (in
   addition to mouse-up's existing click forwarding). The user can now
   start typing the moment they press the page, instead of having to
   first complete a click round-trip to escape the omnibar's focus.

3. Sidecar hover() honors the requesting webview_id instead of
   defaulting to the first webview in the map, so multi-tab sidecars
   no longer pipe every hover into tab #1.

crates/ely_app/src/shell/web_surface_controller.rs

@@ -96,6 +96,14 @@ impl ElyShell {
         }
     }
 
+    /// Hand focus to the shell's root focus handle so subsequent
+    /// keystrokes route to the web surface. Called on the very first
+    /// mouse-down inside an external page so the user can start
+    /// typing without waiting for the click to fully resolve.
+    pub(super) fn focus_web_surface(&self, window: &mut gpui::Window) {
+        self.focus_handle.focus(window);
+    }
+
     pub(super) fn type_text_in_external_web_viewport(
         &mut self,
         tab_id: TabId,