fix(broadcasts): Fix percentage rollout bucketing logic

- Use userId only as seed instead of userId + percentage
- Prevents users from being re-bucketed when rollout % increases
- Ensures deterministic assignment for phased rollouts

services/platform-service/src/modules/broadcasts/targeting.ts

@@ -79,8 +79,9 @@ export function evaluateTarget(
 
   // Percentage rollout (FNV-1a hash for deterministic bucketing)
   if (target.percentageRollout !== undefined && target.percentageRollout < 100) {
-    // Hash userId + broadcast seed for consistent assignment
-    const hash = fnv1a32(`${context.userId}:${target.percentageRollout}`);
+    // Use userId only as seed for consistent bucketing
+    // This ensures when rollout % increases, same users stay included
+    const hash = fnv1a32(context.userId);
     const bucket = hash % 100;
     if (bucket >= target.percentageRollout) {
       return false;