perf(api): eliminate 3 N+1 query patterns

- timeline-holiday-load-support: deduplicate getResolvedCalendarHolidays
  by location key so resources sharing the same country/state/city resolve
  holidays once instead of per-resource
- rate-card-lookup: add lookupRatesBatch that loads rate card lines once
  and scores locally per demand line, replacing per-line DB round-trips
  in estimate-demand-lines autoFillDemandLineRates
- config-readmodels: include _count in utilization-category list query
  instead of calling getById per category for project counts

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

packages/api/src/__tests__/assistant-tools-master-data-management-utilization-read.test.ts

@@ -43,17 +43,9 @@ describe("assistant master data management and utilization read tools", () => {
             description: "Client work",
             isActive: true,
             sortOrder: 1,
+            _count: { projects: 3 },
           },
         ]),
-        findUnique: vi.fn().mockResolvedValue({
-          id: "util_billable",
-          code: "BILLABLE",
-          name: "Billable",
-          description: "Client work",
-          isActive: true,
-          sortOrder: 1,
-          _count: { projects: 3 },
-        }),
       },
     };
     const ctx = createToolContext(db, {
@@ -71,9 +63,6 @@ describe("assistant master data management and utilization read tools", () => {
     expect(db.utilizationCategory.findMany).toHaveBeenCalledWith({
       where: {},
       orderBy: { sortOrder: "asc" },
-    });
-    expect(db.utilizationCategory.findUnique).toHaveBeenCalledWith({
-      where: { id: "util_billable" },
       include: { _count: { select: { projects: true } } },
     });