fix(modal): give the close button a 44px touch target

The close button was 40px square: a 24px icon in 8px of padding. MOBILE.md
sets 44px as the minimum, and the phone filter sheet journey, which
checks every target in the sheet, has failed on it in the staging E2E
gate since the sheet shipped. Measured on staging with the rule
injected: the button is 44x44, nothing in the sheet is under 44, and
the page does not overflow. Every Modal gets the same button, the
compare page's school search included.

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

nextjs-app/components/Modal.module.css

@@ -79,7 +79,11 @@
   font-family: var(--font-display);
 }
 
+/* 44px, the MOBILE.md touch-target minimum: the 24px icon and its padding
+   came to 40, and the phone filter sheet journey caught it. */
 .closeButton {
+  min-width: 2.75rem;
+  min-height: 2.75rem;
   padding: 0.5rem;
   background: transparent;
   border: none;