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/resource-analytics.ts

@@ -26,6 +26,7 @@ export const resourceAnalyticsProcedures = {
     const resources = await ctx.db.resource.findMany({
       where: { isActive: true },
       select: { id: true, displayName: true, chapter: true, skills: true },
+      take: 5000,
     });
 
     const skillMap = new Map<