perf: kill per-row queries on the History tab and Batch Pay preview

- paid_records (History tab) now prefetches work_logs + adjustments:
  the template shows a day-count and loops adjustments per row, which
  fired 2 queries per visible record (~100 on a long history).
- batch_pay_preview replaces the per-worker get_worker_active_team()
  call (worker.teams.filter(...).first() — bypasses prefetch, 1 query
  per worker) with the same batched membership-dict pattern
  payroll_dashboard already uses, and reads the unpaid-adjustments
  check from the existing filtered prefetch instead of .exists().

Also includes (committed earlier in 25910b2 but noting for the record):
the /report/ worker-breakdown loop's per-worker-per-type aggregates
were replaced by one GROUP BY dict (audit fix #7).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/views.py

@@ -3094,9 +3094,13 @@ def payroll_dashboard(request):
             pending_adj_sub_total += worker_adj_sub
 
     # --- Payment history ---
+    # prefetch work_logs + adjustments: the History tab template shows
+    # "{{ record.work_logs.count }} days" and loops record.adjustments.all
+    # per row — without the prefetch that's 2 queries per visible record
+    # (audit fix #9, Jun 2026).
     paid_records = PayrollRecord.objects.select_related(
         'worker'
-    ).order_by('-date', '-id')
+    ).prefetch_related('work_logs', 'adjustments').order_by('-date', '-id')
 
     # --- Recent payments total (last 60 days, inclusive) ---
     # 60-day window math: subtract 59 days, not 60. With `>=` that yields
@@ -3952,8 +3956,22 @@ def batch_pay_preview(request):
         ),
     ).order_by('name')
 
+    # === Active team per worker — ONE batched membership query ===
+    # get_worker_active_team() runs worker.teams.filter(...).first() per
+    # worker, which bypasses the prefetch cache and fired a query per row
+    # (audit fix #10, Jun 2026). Same dict pattern as payroll_dashboard.
+    active_team_by_id = {t.id: t for t in Team.objects.filter(active=True)}
+    worker_active_team = {}
+    for membership in Team.workers.through.objects.filter(
+        team_id__in=active_team_by_id.keys()
+    ).values('team_id', 'worker_id'):
+        wid = membership['worker_id']
+        if wid in worker_active_team:
+            continue
+        worker_active_team[wid] = active_team_by_id[membership['team_id']]
+
     for worker in active_workers:
-        team = get_worker_active_team(worker)
+        team = worker_active_team.get(worker.id)
 
         # --- In 'schedule' mode, skip workers without a pay schedule ---
         if mode == 'schedule':
@@ -3966,7 +3984,9 @@ def batch_pay_preview(request):
                         has_unpaid = True
                         break
                 if not has_unpaid:
-                    has_unpaid = worker.adjustments.filter(payroll_record__isnull=True).exists()
+                    # the adjustments prefetch above is already filtered to
+                    # unpaid rows — bool() reads the cache, no extra query
+                    has_unpaid = bool(worker.adjustments.all())
 
                 if has_unpaid:
                     skipped.append({