feat: add AssetModel Prisma model + migration

prisma/schema.prisma

@@ -242,6 +242,13 @@ model AssetCategory {
   valueGroup    AssetCategoryValueGroup      @map("value_group")
   createdAt     DateTime                     @default(now()) @map("created_at") @db.Timestamptz(6)
   attributeDefs AssetCategoryAttributeDef[]
+  // Back-relation for AssetModel.categoryId — see "Cập nhật 2026-08-02 (2)"
+  // in docs/asset-license-management.md. Only categories with
+  // valueGroup=high_value are ever actually referenced by an AssetModel (a
+  // business rule enforced in src/lib/asset-models.ts's createAssetModel(),
+  // not expressible as a Prisma-level constraint), but the relation itself
+  // is not restricted to high_value categories at the schema level.
+  assetModels   AssetModel[]
 
   @@map("asset_categories")
 }
@@ -293,6 +300,37 @@ model AssetCategoryAttributeDef {
   @@map("asset_category_attribute_defs")
 }
 
+// Sits between AssetCategory and AssetItem — see docs/
+// asset-license-management.md's "Cập nhật 2026-08-02 (2)" section and the
+// `AssetModel` row in the "Data model (sơ bộ)" table. 1 AssetModel has many
+// AssetItem serials (AssetItem.modelId FK, not built in this task).
+// `manufacturer`/`name` are deliberately two separate String fields (not
+// merged into one), per the doc, to allow filtering/reporting by
+// manufacturer alone (e.g. "Dell") without string-parsing a combined field.
+// `categoryId` is a required FK to AssetCategory — the DB layer doesn't
+// enforce that the referenced category is `high_value` (Prisma/Postgres FK
+// constraints can't express that), that business rule is checked in
+// src/lib/asset-models.ts's createAssetModel() via an explicit lookup
+// before the create, per the doc's "Ràng buộc dữ liệu" section. `specs` is
+// JSONB, defaulting to an empty object — the real per-category dynamic
+// attribute *values* (whose *shape* is defined by
+// AssetCategoryAttributeDef rows for this model's category). This task
+// deliberately does NOT validate specs against the category's attribute
+// defs (loose z.record(z.unknown()) validation only, see
+// src/lib/asset-models.ts) — that dynamic cross-validation is a separate
+// follow-up task per the doc's "Cập nhật 2026-08-02 (3)" section.
+model AssetModel {
+  id           String        @id @default(uuid()) @db.Uuid
+  categoryId   String        @map("category_id") @db.Uuid
+  category     AssetCategory @relation(fields: [categoryId], references: [id])
+  manufacturer String
+  name         String
+  specs        Json          @default("{}")
+  createdAt    DateTime      @default(now()) @map("created_at") @db.Timestamptz(6)
+
+  @@map("asset_models")
+}
+
 // Minimal internal auth accounts — NOT company SSO (deliberately ruled out,
 // see CLAUDE.md / auth decision notes). A handful of trusted IT staff
 // accounts, created by hand via scripts/create-user.ts, no self-registration.