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.tsx

@@ -834,6 +834,18 @@ export function HomeView({ initialSchools, filters, totalSchools, howItWorks, ed
                       setSelectedMapSchool(school);
                     }}
                   >
+                    {/* The keyboard's way to pick the pin: hidden until it has
+                        focus, since a pointer just clicks the row. The row
+                        itself cannot be the button, as it holds links and
+                        buttons of its own. */}
+                    <button
+                      type="button"
+                      className={styles.showOnMap}
+                      aria-pressed={selectedMapSchool?.urn === school.urn}
+                      onClick={() => setSelectedMapSchool(school)}
+                    >
+                      Show {school.school_name} on the map
+                    </button>
                     {renderRow(school)}
                   </div>
                 ))}