feat: add License Prisma model + migration

prisma/schema.prisma

@@ -92,6 +92,36 @@ model AssetItem {
   @@map("asset_items")
 }
 
+// Fixed, closed set of 2 values tied to the domain (see docs/
+// asset-license-management.md's "Data model (sơ bộ)" table) — native
+// Postgres enum, same rationale as RequestType/AssetItemStatus above.
+enum LicenseType {
+  perpetual
+  subscription
+}
+
+// Software license inventory — see docs/asset-license-management.md's "Data
+// model (sơ bộ)" table (tên, vendor, tổng seat, seat đã dùng, ngày hết hạn,
+// loại). `vendor` is deliberately a plain String for now, not a separate
+// Vendor entity — no Vendor entity exists yet, same "plain string for now"
+// precedent as Employee.department. `seatsUsed` is a stored counter
+// (defaults to 0 at creation), not a computed value — it will only ever be
+// set to 0 here since Assignment (the thing that would consume seats)
+// doesn't exist yet. `expiryDate` is nullable: perpetual licenses never
+// expire, only subscription licenses usually have one.
+model License {
+  id          String      @id @default(uuid()) @db.Uuid
+  name        String
+  vendor      String
+  seatsTotal  Int         @map("seats_total")
+  seatsUsed   Int         @default(0) @map("seats_used")
+  expiryDate  DateTime?   @map("expiry_date") @db.Date
+  licenseType LicenseType @map("license_type")
+  createdAt   DateTime    @default(now()) @map("created_at") @db.Timestamptz(6)
+
+  @@map("licenses")
+}
+
 // 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.