fix(chrome): name a web field by its hint, not its CSS class

visibleLabel reads hintText first for an editable element. The dump never
emitted it, so an empty web input fell through text, description and
descendant text to its class name, and the model was shown an identifier no
user can read on exactly the fields a labelling experiment varies.

Same ladder as fieldHint in web-runtime.ts, so one field is named one way on
both hosts.

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

internal/driver/chrome/testdata/fact-parity-shadow.html

@@ -25,7 +25,7 @@
         <div id="shadow-overlay">
           <button id="shadow-save">save</button>
           <button id="shadow-cancel" disabled>cancel</button>
-          <input id="shadow-amount" type="text" value="10" />
+          <input id="shadow-amount" type="text" value="10" placeholder="0.00" />
           <div id="shadow-plain">plain</div>
         </div>
         <div id="shadow-scroller"><div id="shadow-scroller-content"></div></div>`;