fix(diff): correct array concatenation in getVariationDiff

Fix operator precedence issue where || had higher precedence than concat,
causing the array to not be properly concatenated. Wrap the left operand
in parentheses to ensure correct evaluation order.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: talissoncosta

frontend/web/components/diff/diff-utils.ts

@@ -167,8 +167,9 @@ export const getVariationDiff = (
 ) => {
   let totalChanges = 0
   const variationOptions = uniqBy(
-    oldFeatureState?.multivariate_feature_state_values ||
-      [].concat(newFeatureState?.multivariate_feature_state_values || []),
+    (oldFeatureState?.multivariate_feature_state_values || []).concat(
+      newFeatureState?.multivariate_feature_state_values || [],
+    ),
     (v) => v.multivariate_feature_option,
   )
   const diffs = variationOptions.map((variationOption) => {