fix(test-definitions): import Tooltip in Link and drop external-URL underline

Address review feedback on the click-through link:

- Link referenced Tooltip without importing it, so any Link given a `tooltip`
  (the test-results external-link cell) threw at render. Import it from
  tooltip.js.
- In the result test-definition summary, the external URL used `underline` plus
  a full-width link, so the hover underline spanned the panel and read as a
  divider. Drop the underline (the open_in_new icon is enough affordance) and
  size the link to content (max-width instead of width) so long URLs still wrap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: aarthy-dk

testgen/ui/components/frontend/js/pages/test_definition_summary.js

@@ -126,7 +126,6 @@ const TestDefinitionSummary = (props) => {
                                 href: testDefinition.external_url.trim(),
                                 label: testDefinition.external_url.trim(),
                                 open_new: true,
-                                underline: true,
                                 right_icon: 'open_in_new',
                                 right_icon_size: 16,
                             })
@@ -174,7 +173,6 @@ stylesheet.replace(`
     overflow-wrap: anywhere;
 }
 .external-url-attribute .tg-link {
-    width: 100%;
     max-width: 100%;
 }
 .external-url-attribute .tg-link--wrapper {

testgen/ui/static/js/components/link.js

@@ -20,6 +20,7 @@
  * @property {((event: any) => void)?} onClick
  */
 import { getValue, loadStylesheet } from '../utils.js';
+import { Tooltip } from './tooltip.js';
 import van from '../van.min.js';
 
 const { a, div, i, span } = van.tags;