fix: remove premature updateClusterAfterMerge call in merge loop

Critical bug fix:
- updateClusterAfterMerge() was called after EACH trace merge
- This caused source group to be deleted after first trace
- Remaining traces had no group to merge into

Problem flow:
1. Merge trace #1 from Group B → Group A
2. updateClusterAfterMerge(B, A) deletes Group B
3. Try to merge trace #2 from Group B → Group B is gone!
4. Result: All source groups deleted after first trace

Solution:
- Remove updateClusterAfterMerge() from loop
- Let all traces merge successfully
- Reload cluster data at the end (Line 1813)
- Core API handles the merge, we just refresh UI

Impact:
- Merge now works correctly for all traces in a group
- No premature deletion of source groups
- UI refreshes after all operations complete

src/views/PeopleView.vue

@@ -1796,7 +1796,6 @@ async function executeMerge(targetGroupId: string) {
           target_id: targetTraceId 
         })
         successCount++
-        updateClusterAfterMerge(g.identity_uuid, targetGroupId)
       } catch (e) {
         console.error('Merge trace failed:', srcTraceId, e)
         failCount++