fix(compare): repair the mobile add-school modal

The 'add school' modal passed no title to Modal, so its header held only
the close button — shoved to the far left by justify-content:space-between
in an otherwise-empty bar — while the real title was rendered separately
inside the content. Pass the title to Modal so the header reads title
(left) + close (right), and drop the duplicate in-content heading.

Also: the mobile full-width result button targeted a dead .addButton
selector (the button never had that class), so it rendered inconsistently
— give the button a real module class and full width on mobile, tighten
the stacked cards, and give the bottom sheet a stable min-height so its
empty state isn't a tiny stub.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

nextjs-app/components/Modal.module.css

@@ -123,6 +123,10 @@
   .modal {
     width: 100%;
     max-width: 100%;
+    /* Bottom sheet: open at a stable, comfortable height so the empty
+       "start typing" state isn't a tiny stub and the sheet doesn't jump as
+       results load (the results list scrolls within). */
+    min-height: 55vh;
     max-height: 95vh;
     border-bottom-left-radius: 0;
     border-bottom-right-radius: 0;