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.html

@@ -52,7 +52,16 @@
       <option id="choice-first">first</option>
     </select>
     <input id="amount" type="text" value="10" />
-    <input id="agree" type="checkbox" />
+    <!-- One field per rung of the hint ladder both producers name an editable
+         field by. A rung read on one side only sends the model a different name
+         for the same field on the two hosts, which is the observation channel
+         the label-source arms vary. -->
+    <label id="hint-label-text" for="hint-label">Amount</label>
+    <input id="hint-label" type="text" placeholder="0.00" name="amount-field" />
+    <input id="hint-aria" type="text" aria-label="Search" placeholder="Type here" name="q" />
+    <input id="hint-placeholder" type="text" placeholder="What's this for?" name="note-field" />
+    <input id="hint-name" type="text" name="reference-field" />
+    <input id="agree" type="checkbox" placeholder="not a hint" />
     <textarea id="notes"></textarea>
     <div id="bio" contenteditable="true">bio</div>
     <div id="menu" role="button">menu</div>