feat(server): 工作流扩展 leave 实体骨架（F24）

- workflow_instances 解耦 reimbursement FK：新增 reimbursement_id/leave_request_id + 回填迁移
- 新增 leave_requests 表与 /api/leave-requests 最小链路（create/submit）
- workflow approve/reject/return 支持 leave 状态更新；transfer 非报销任务禁用
- seed-config 增加 leave workflow definition；更新 v3 CSV 状态推进

server/prisma/migrations/20260209131639_workflow_instance_multi_entity_leave/migration.sql

@@ -0,0 +1,56 @@
+-- CreateEnum
+CREATE TYPE "LeaveRequestStatus" AS ENUM ('draft', 'reviewing', 'approved', 'rejected', 'cancelled');
+
+-- DropForeignKey
+ALTER TABLE "workflow_instances" DROP CONSTRAINT "workflow_instances_entity_id_fkey";
+
+-- AlterTable
+ALTER TABLE "workflow_instances" ADD COLUMN     "leave_request_id" UUID,
+ADD COLUMN     "reimbursement_id" UUID;
+
+-- CreateTable
+CREATE TABLE "leave_requests" (
+    "id" UUID NOT NULL,
+    "owner_id" UUID NOT NULL,
+    "department_id" UUID NOT NULL,
+    "start_date" DATE NOT NULL,
+    "end_date" DATE NOT NULL,
+    "reason" TEXT,
+    "status" "LeaveRequestStatus" NOT NULL DEFAULT 'draft',
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "created_by" UUID,
+    "updated_at" TIMESTAMP(3) NOT NULL,
+    "updated_by" UUID,
+
+    CONSTRAINT "leave_requests_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "leave_requests_owner_id_idx" ON "leave_requests"("owner_id");
+
+-- CreateIndex
+CREATE INDEX "leave_requests_department_id_idx" ON "leave_requests"("department_id");
+
+-- CreateIndex
+CREATE INDEX "leave_requests_status_idx" ON "leave_requests"("status");
+
+-- CreateIndex
+CREATE INDEX "idx_leave_owner_status_updated_at" ON "leave_requests"("owner_id", "status", "updated_at");
+
+-- CreateIndex
+CREATE INDEX "workflow_instances_reimbursement_id_idx" ON "workflow_instances"("reimbursement_id");
+
+-- CreateIndex
+CREATE INDEX "workflow_instances_leave_request_id_idx" ON "workflow_instances"("leave_request_id");
+
+-- AddForeignKey
+ALTER TABLE "leave_requests" ADD CONSTRAINT "leave_requests_owner_id_fkey" FOREIGN KEY ("owner_id") REFERENCES "employees"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "leave_requests" ADD CONSTRAINT "leave_requests_department_id_fkey" FOREIGN KEY ("department_id") REFERENCES "departments"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "workflow_instances" ADD CONSTRAINT "workflow_instances_reimbursement_id_fkey" FOREIGN KEY ("reimbursement_id") REFERENCES "reimbursement_forms"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "workflow_instances" ADD CONSTRAINT "workflow_instances_leave_request_id_fkey" FOREIGN KEY ("leave_request_id") REFERENCES "leave_requests"("id") ON DELETE CASCADE ON UPDATE CASCADE;

server/prisma/migrations/20260209131830_workflow_instance_backfill_entity_links/migration.sql

@@ -0,0 +1,12 @@
+-- Backfill workflow_instances.*_id columns for existing rows.
+-- Reimbursement instances historically used entity_id as FK target.
+UPDATE "workflow_instances"
+SET reimbursement_id = entity_id
+WHERE entity_type = 'reimbursement'
+  AND reimbursement_id IS NULL;
+
+UPDATE "workflow_instances"
+SET leave_request_id = entity_id
+WHERE entity_type = 'leave'
+  AND leave_request_id IS NULL;
+