feat: add MaintenanceRecord Prisma model + migration

New entity tracking repair/warranty/preventive maintenance jobs for an
AssetItem. Reuses Vendor (nullable) for the repair location, no cost
field (mirrors PurchaseOrder). "At most 1 open record per AssetItem"
invariant left to the application layer, mirroring Assignment.

prisma/migrations/20260804092355_add_maintenance_record/migration.sql

@@ -0,0 +1,23 @@
+-- CreateEnum
+CREATE TYPE "MaintenanceType" AS ENUM ('repair', 'warranty', 'preventive');
+
+-- CreateTable
+CREATE TABLE "maintenance_records" (
+    "id" UUID NOT NULL,
+    "asset_item_id" UUID NOT NULL,
+    "type" "MaintenanceType" NOT NULL,
+    "vendor_id" UUID,
+    "issue_description" TEXT NOT NULL,
+    "resolution_notes" TEXT,
+    "start_date" DATE NOT NULL,
+    "end_date" DATE,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "maintenance_records_pkey" PRIMARY KEY ("id")
+);
+
+-- AddForeignKey
+ALTER TABLE "maintenance_records" ADD CONSTRAINT "maintenance_records_asset_item_id_fkey" FOREIGN KEY ("asset_item_id") REFERENCES "asset_items"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "maintenance_records" ADD CONSTRAINT "maintenance_records_vendor_id_fkey" FOREIGN KEY ("vendor_id") REFERENCES "vendors"("id") ON DELETE SET NULL ON UPDATE CASCADE;