perf(api): eliminate N+1 queries, add query guards and missing indexes

- Notification fan-out: replace sequential for loops with Promise.all (allocation-effects, notification-broadcast, create-notification)
- Public holiday batch: group resources by location combo, resolve holidays once per group, replace per-holiday delete/findFirst/create with 3 batched queries (~18K → ~5 queries)
- Add take guards to unbounded findMany calls (resource-analytics: 5000, resource-marketplace: 2000, resource-capacity: 1000, chargeability-report: 2000)
- auto-staffing: add select with only needed fields + take: 5000
- schema.prisma: add 5 missing indexes (ManagementLevel.groupId, Blueprint.isActive/target, Comment.parentId, Vacation.requestedById, Resource.managementLevelGroupId)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/api/src/router/notification-broadcast-procedure-support.ts

@@ -117,27 +117,28 @@ async function persistImmediateBroadcast(
     data: buildBroadcastCreateData(senderId, input),
   });
 
-  const notificationIds: BroadcastRecipientNotification[] = [];
-  for (const recipientUserId of recipientIds) {
-    const notificationId = await createNotification({
-      db,
-      userId: recipientUserId,
-      type: `BROADCAST_${input.category}`,
-      title: input.title,
-      body: input.body,
-      link: input.link,
-      category: input.category,
-      priority: input.priority,
-      channel: input.channel,
-      sourceId: broadcast.id,
-      senderId,
-      taskStatus: isTask ? "OPEN" : undefined,
-      taskAction: input.taskAction,
-      dueDate: input.dueDate,
-      emit: false,
-    });
-    notificationIds.push({ id: notificationId, userId: recipientUserId });
-  }
+  const created = await Promise.all(
+    recipientIds.map((recipientUserId) =>
+      createNotification({
+        db,
+        userId: recipientUserId,
+        type: `BROADCAST_${input.category}`,
+        title: input.title,
+        body: input.body,
+        link: input.link,
+        category: input.category,
+        priority: input.priority,
+        channel: input.channel,
+        sourceId: broadcast.id,
+        senderId,
+        taskStatus: isTask ? "OPEN" : undefined,
+        taskAction: input.taskAction,
+        dueDate: input.dueDate,
+        emit: false,
+      }),
+    ),
+  );
+  const notificationIds: BroadcastRecipientNotification[] = created.map((id, i) => ({ id, userId: recipientIds[i]! }));
 
   const updatedBroadcast = await db.notificationBroadcast.update({
     where: { id: broadcast.id },