feat(mobile): hide ComparisonToast — Compare tab badge replaces it

MOB-05: With the bottom tab bar's Compare badge now showing the
selected count and providing one-tap navigation to /compare, the
floating toast becomes redundant chrome on phones — it cost ~70px
of permanent vertical space and visually competed with the tab bar
right above it. Hide at ≤640px. Per-school removal still works on
the /compare page itself. Desktop unaffected.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

nextjs-app/components/ComparisonToast.module.css

@@ -167,21 +167,12 @@
   background: var(--accent-coral-dark, #c9614a);
 }
 
+/* Hidden on phones — the bottom tab bar's Compare badge already
+   communicates count + destination, so the toast becomes redundant
+   chrome that costs ~70px of permanent vertical space. Per-school
+   removal still lives on the /compare page itself. */
 @media (max-width: 640px) {
   .toastContainer {
-    /* Sit above the fixed bottom tab bar (56px + safe-area inset) */
-    bottom: calc(56px + env(safe-area-inset-bottom, 0px) + 0.75rem);
-    width: calc(100% - 2rem);
-  }
-
-  .toastContent {
-    gap: 0;
-    border-radius: 16px;
-    padding: 1.25rem;
-  }
-
-  .toastActions {
-    width: 100%;
-    justify-content: space-between;
+    display: none;
   }
 }