style(buttons): standardise button sizes across all components

Define two button tiers and apply consistently:
- sm (inline pairs): padding 0.5rem 1rem, font-size 0.875rem, radius 6px
- md (standalone CTAs): padding 0.625rem 1.25rem, font-size 0.9rem, radius 8px

RankingsView: viewButton was 0.25rem/0.8rem/4px vs addButton 0.5rem/0.875rem/8px
— biggest mismatch, both now sm with same radius.
SchoolCard: horizontal padding 0.75rem → 1rem, font-size 0.8125rem → 0.875rem.
SchoolRow: padding 0.4375rem → 0.5rem to match sm exactly.
SchoolDetailView: font-size 0.8125rem → 0.875rem.
ComparisonView/Modal: addButton and shareButton aligned to md spec.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nextjs-app/components/ComparisonView.module.css

@@ -31,8 +31,8 @@
 }
 
 .addButton {
-  padding: 0.75rem 1.5rem;
-  font-size: 0.9375rem;
+  padding: 0.625rem 1.25rem;
+  font-size: 0.9rem;
   font-weight: 600;
   background: var(--accent-coral, #e07256);
   color: white;
@@ -370,12 +370,13 @@
   display: inline-flex;
   align-items: center;
   gap: 0.375rem;
-  padding: 0.5rem 1rem;
+  padding: 0.625rem 1.25rem;
   background: var(--bg-secondary);
   border: 1px solid var(--border-color, #e0ddd8);
-  border-radius: var(--radius-md);
+  border-radius: 8px;
   color: var(--text-secondary);
-  font-size: 0.875rem;
+  font-size: 0.9rem;
+  font-weight: 600;
   cursor: pointer;
   transition: all var(--transition);
 }