fix: alpha sort by labelPlural primary, symbol secondary

Handles ties like 'Barrel (US fluid)' vs 'Barrel (US dry)'

src/routes/+page.svelte

@@ -153,7 +153,10 @@
       const items = byGroup.get(group.id);
       if (items?.length) {
         const sorted = group.sortOrder === 'alpha'
-          ? [...items].sort((a, b) => a.unit.label.localeCompare(b.unit.label))
+          ? [...items].sort((a, b) => {
+              const labelCmp = a.unit.labelPlural.localeCompare(b.unit.labelPlural);
+              return labelCmp !== 0 ? labelCmp : a.unit.symbol.localeCompare(b.unit.symbol);
+            })
           : items;
         sections.push({ groupLabel: group.label, alwaysShowLabel: group.alwaysShowLabel ?? false, items: sorted });
       }