Stop hijacking omnibar typing when an external web tab is active

Real bug found by reading capture_key_down semantics: the web
keyboard handler was registered as `capture_key_down` on the root
div, which fires from root → focused element. So when the user is
on an external tab (https://google.com) and clicks the omnibar to
type a new URL, every keystroke was intercepted at the root, the
text was forwarded to Servo, and `cx.stop_propagation()` killed the
event before it could reach the focused Input. The omnibar appeared
dead.

Gate the handler on `self.focus_handle.is_focused(window)`. The
shell's root handle is only focused when nothing deeper is — clicks
on the web viewport call `focus_handle.focus(window)`, which makes
the root focused; clicks on any Input transfer focus to the Input's
handle and `is_focused` returns false on the root. Now keystrokes
reach the Input untouched while still flowing to Servo when the
user is interacting with the page itself.

cargo test --workspace: 440 passed, 0 failed.

crates/ely_app/src/shell/web_surface_keyboard.rs

@@ -7,9 +7,22 @@ impl ElyShell {
     pub(super) fn on_external_web_key_down(
         &mut self,
         event: &KeyDownEvent,
-        _window: &mut Window,
+        window: &mut Window,
         cx: &mut Context<Self>,
     ) {
+        // Only forward keys to the web viewport when the shell's root
+        // focus handle is the one that's actually focused. If the user
+        // has clicked the omnibar Input (or any other Input — plugin
+        // search, bookmark editor, etc.), focus has moved to that
+        // Input's handle and the user expects keystrokes to reach it.
+        // Without this guard, capture_key_down on the root would
+        // intercept every keystroke and forward it to Servo, leaving
+        // the omnibar permanently dead while any external tab is
+        // active.
+        if !self.focus_handle.is_focused(window) {
+            return;
+        }
+
         let Some((tab_id, requested_url)) = self.active_external_tab_target() else {
             return;
         };