fix(search): address review on the shared result rows

- The rows' narrow layout now switches at a 608px list, not 600px. Below
  769px the page pads 1rem each side, so a 640px screen gives a 608px
  list: exactly the old max-width: 640px media query, where 600px left
  633-640px screens on the wide layout.
- rowContainerGuard.test.ts fails if anything other than HomeView renders
  SchoolRow or SecondarySchoolRow, or if one of HomeView's row lists loses
  its `results` container. Outside one the rows silently keep their wide
  layout on phones. (Checked: HomeView is the only importer today.)
- Picking a pin from the list beside the map now works from the keyboard:
  each row carries a "Show <school> on the map" button, visually hidden
  until focused, with aria-pressed for the selected school. The row itself
  cannot be the button, since it holds links and buttons of its own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

nextjs-app/components/HomeView.module.css

@@ -638,15 +638,46 @@
 
 /* A row in the list beside the map: clicking it picks its pin. */
 .mapRow {
+  position: relative;
   cursor: pointer;
   border-radius: 10px;
 }
 
-.mapRowSelected > * {
+.mapRowSelected > :last-child {
   outline: 2px solid var(--brand);
   outline-offset: 1px;
 }
 
+/* Visually hidden until focused, then a pill over the row's top edge. */
+.showOnMap {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  overflow: hidden;
+  clip-path: inset(50%);
+  white-space: nowrap;
+}
+
+.showOnMap:focus-visible {
+  top: -0.5rem;
+  right: 0.75rem;
+  z-index: 1;
+  width: auto;
+  height: auto;
+  padding: 0.375rem 0.75rem;
+  overflow: visible;
+  clip-path: none;
+  background: var(--brand);
+  color: var(--brand-on);
+  border: 0;
+  border-radius: 999px;
+  font-family: var(--font-ui);
+  font-size: var(--step--1);
+  font-weight: 700;
+  outline: 2px solid var(--text-primary);
+  outline-offset: 2px;
+}
+
 
 
 .sectionHeader {