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/SchoolRow.module.css

@@ -129,7 +129,7 @@
 }
 
 .btnView {
-  padding: 0.4375rem 0.875rem;
+  padding: 0.5rem 1rem;
   font-size: 0.875rem;
   font-weight: 500;
   color: var(--text-secondary, #5c564d);
@@ -147,7 +147,7 @@
 }
 
 .btnCompare {
-  padding: 0.4375rem 0.875rem;
+  padding: 0.5rem 1rem;
   font-size: 0.875rem;
   font-weight: 600;
   color: white;
@@ -164,7 +164,7 @@
 }
 
 .btnRemove {
-  padding: 0.4375rem 0.875rem;
+  padding: 0.5rem 1rem;
   font-size: 0.875rem;
   font-weight: 500;
   color: var(--text-secondary, #5c564d);
@@ -272,8 +272,8 @@
   .btnView,
   .btnCompare,
   .btnRemove {
-    padding: 0.375rem 0.75rem;
-    font-size: 0.8125rem;
+    padding: 0.4375rem 0.875rem;
+    font-size: 0.875rem;
   }
 
   .rowProgress {