refactor(application): extract vacation management into application use-cases

Moves approve, reject, cancel, and request vacation business logic
out of the tRPC procedure layer into packages/application, matching
the pattern used by allocation use-cases.

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

packages/application/src/use-cases/vacation/index.ts

@@ -0,0 +1,29 @@
+export {
+  approveVacation,
+  batchApproveVacations,
+  type ApproveVacationInput,
+  type ApproveVacationResult,
+  type ApproveVacationDeps,
+  type BatchApproveVacationInput,
+  type BatchApproveVacationResult,
+  type BatchApproveVacationDeps,
+  type VacationChargeableInput,
+} from "./approve-vacation.js";
+
+export {
+  rejectVacation,
+  batchRejectVacations,
+  type RejectVacationInput,
+  type RejectVacationResult,
+  type RejectVacationDeps,
+  type BatchRejectVacationInput,
+  type BatchRejectVacationResult,
+  type BatchRejectVacationDeps,
+} from "./reject-vacation.js";
+
+export {
+  cancelVacation,
+  type CancelVacationInput,
+  type CancelVacationResult,
+  type CancelVacationDeps,
+} from "./cancel-vacation.js";