Truncate grid display to 4 characters for VUCC awards

For VUCC awards, ensure the grid square is truncated to 4 characters
both when counting unique entities AND when displaying.

This fixes VUCC award details to show 'FN31' instead of 'FN31pr',
making it clear that we're counting unique 4-character grid squares.

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

src/backend/services/awards.service.js

@@ -283,7 +283,12 @@ export async function getAwardEntityBreakdown(userId, awardId) {
       // Use displayField from award rules, or fallback to entity/type
       let displayName = String(entity);
       if (rules.displayField) {
-        displayName = String(qso[rules.displayField] || entity);
+        let rawValue = qso[rules.displayField];
+        // For grid-based awards, truncate to first 4 characters
+        if (rules.displayField === 'grid' && rawValue && rawValue.length > 4) {
+          rawValue = rawValue.substring(0, 4);
+        }
+        displayName = String(rawValue || entity);
       } else {
         // Fallback: try entity, state, grid, callsign in order
         displayName = qso.entity || qso.state || qso.grid || qso.callsign || String(entity);