Group metrics dropdown by category in rankings and comparison views

Added optgroup elements to organize metrics into logical categories:
- Expected Standard
- Higher Standard
- Progress Scores
- Average Scores
- Gender Performance
- Equity (Disadvantaged)
- School Context
- 3-Year Trends

Also added CSS styling for optgroup labels to match the design system.

Note: School names in rankings are already clickable links to school details.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nextjs-app/components/ComparisonView.tsx

@@ -140,11 +140,46 @@ export function ComparisonView({
           onChange={(e) => handleMetricChange(e.target.value)}
           className={styles.metricSelect}
         >
-          {metrics.map((metric) => (
-            <option key={metric.key} value={metric.key}>
-              {metric.label}
-            </option>
-          ))}
+          <optgroup label="Expected Standard">
+            {metrics.filter(m => m.category === 'expected').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="Higher Standard">
+            {metrics.filter(m => m.category === 'higher').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="Progress Scores">
+            {metrics.filter(m => m.category === 'progress').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="Average Scores">
+            {metrics.filter(m => m.category === 'average').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="Gender Performance">
+            {metrics.filter(m => m.category === 'gender').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="Equity (Disadvantaged)">
+            {metrics.filter(m => m.category === 'equity').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="School Context">
+            {metrics.filter(m => m.category === 'context').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
+          <optgroup label="3-Year Trends">
+            {metrics.filter(m => m.category === 'trends').map((metric) => (
+              <option key={metric.key} value={metric.key}>{metric.label}</option>
+            ))}
+          </optgroup>
         </select>
       </section>