feat: add AssetCategoryAttributeDef Prisma model + migration

Per-category dynamic attribute definitions (key/label/dataType/required/
sortOrder), FK to AssetCategory, composite unique (categoryId, key) so the
same key is allowed across different categories but not duplicated within
one. dataType is a new closed Prisma enum (AssetAttributeDataType), a
dev-defined technical set distinct from AssetCategoryValueGroup.

prisma/migrations/20260803003747_add_asset_category_attribute_def/migration.sql

@@ -0,0 +1,22 @@
+-- CreateEnum
+CREATE TYPE "AssetAttributeDataType" AS ENUM ('string', 'number', 'boolean', 'date');
+
+-- CreateTable
+CREATE TABLE "asset_category_attribute_defs" (
+    "id" UUID NOT NULL,
+    "category_id" UUID NOT NULL,
+    "key" TEXT NOT NULL,
+    "label" TEXT NOT NULL,
+    "data_type" "AssetAttributeDataType" NOT NULL,
+    "required" BOOLEAN NOT NULL,
+    "sort_order" INTEGER NOT NULL,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "asset_category_attribute_defs_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "asset_category_attribute_defs_category_id_key_key" ON "asset_category_attribute_defs"("category_id", "key");
+
+-- AddForeignKey
+ALTER TABLE "asset_category_attribute_defs" ADD CONSTRAINT "asset_category_attribute_defs_category_id_fkey" FOREIGN KEY ("category_id") REFERENCES "asset_categories"("id") ON DELETE RESTRICT ON UPDATE CASCADE;