feat: support cross-origin iframe snapshots and interactions via Target.setAutoAttach (#949)

* feat: support cross-origin iframe snapshots and interactions via Target.setAutoAttach (#925)

Enable Target.setAutoAttach with flatten: true on page sessions so Chrome
auto-creates dedicated CDP sessions for cross-origin iframe targets.

- Add DrainedEvents struct, iframe_sessions map, attach/detach event handling
- Extract resolve_ax_session (shared) and resolve_frame_session helpers
- resolve_element_object_id returns (object_id, effective_session) tuple
- resolve_element_center returns (x, y, effective_session) tuple
- Input dispatch (click/hover/tap) uses effective session for correct coordinates
- Thread iframe_sessions through element.rs, interaction.rs, screenshot.rs
- Clear iframe sessions on navigate, tab switch, tab new, tab close
- Ignore Target.setAutoAttach failure for non-Chrome backends (Lightpanda)
- Unit tests for session resolution logic

* fix

* fix

* fix

---------

Co-authored-by: hyunjinee <leehj0110@kakao.com>

cli/src/native/browser.rs

@@ -420,6 +420,21 @@ impl BrowserManager {
         self.client
             .send_command_no_params("Network.enable", Some(session_id))
             .await?;
+        // Enable auto-attach for cross-origin iframe support.
+        // flatten: true gives each iframe its own session_id.
+        // Ignored on engines that don't support it (e.g. Lightpanda).
+        let _ = self
+            .client
+            .send_command(
+                "Target.setAutoAttach",
+                Some(json!({
+                    "autoAttach": true,
+                    "waitForDebuggerOnStart": false,
+                    "flatten": true
+                })),
+                Some(session_id),
+            )
+            .await;
         Ok(())
     }