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/__tests__/notification-router.test.ts

@@ -665,7 +665,8 @@ describe("notification.createBroadcast", () => {
 
     expect(transaction).toHaveBeenCalledTimes(1);
     expect(txCreateBroadcast).toHaveBeenCalledTimes(1);
-    expect(txCreateNotification).toHaveBeenCalledTimes(1);
+    // Parallel fan-out: both recipients are attempted concurrently
+    expect(txCreateNotification).toHaveBeenCalledTimes(2);
     expect(txUpdateBroadcast).not.toHaveBeenCalled();
     expect(outerCreateBroadcast).not.toHaveBeenCalled();
     expect(outerUpdateBroadcast).not.toHaveBeenCalled();