fix(chrome): emit editable as a plain boolean

editable was emitted as `isEditable || null`, and an absent field sends
internal/hierarchy into the native fallback, which reads any class name
containing "EditText" as an Android text widget. On web that is just a CSS
class, so a page styling a div with it was editable to the goja host and not to
the web runtime, and the model policy could be offered typing into a div.

Claude-Session: https://claude.ai/code/session_01A5KmftdEJ49A9z5mF5ESrX

internal/driver/chrome/driver.go

@@ -414,7 +414,12 @@ func (d *Driver) Hierarchy(ctx context.Context) (string, error) {
       focused: document.activeElement === el || null,
       checked: el.checked || null,
       selected: el.selected || null,
-      editable: isEditable || null,
+      // Emitted as a plain boolean, never null: internal/hierarchy falls back to
+      // the native heuristic when the field is absent, which reads any class
+      // name containing "EditText" as an Android text widget. On web that is a
+      // CSS class, so a page styling a div with it made the goja host offer
+      // typing into a div the web runtime never calls editable.
+      editable: isEditable,
     };
   }
   // Rooted at documentElement, not body, because collectTargets in