feat: implement i18n for product and category, add 5 new locales

apps/backend/prisma/migrations/20260614010000_add_category_translation/migration.sql

@@ -0,0 +1,22 @@
+-- CreateTable
+CREATE TABLE "CategoryTranslation" (
+    "id" SERIAL NOT NULL,
+    "categoryId" INTEGER NOT NULL,
+    "langCode" TEXT NOT NULL,
+    "name" TEXT NOT NULL,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "CategoryTranslation_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "CategoryTranslation_categoryId_langCode_key" ON "CategoryTranslation"("categoryId", "langCode");
+
+-- AddForeignKey
+ALTER TABLE "CategoryTranslation" ADD CONSTRAINT "CategoryTranslation_categoryId_fkey" FOREIGN KEY ("categoryId") REFERENCES "Category"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- Seed Thai translations from existing category names
+INSERT INTO "CategoryTranslation" ("categoryId", "langCode", "name", "updatedAt")
+SELECT id, 'th', name, NOW() FROM "Category"
+ON CONFLICT ("categoryId", "langCode") DO NOTHING;

apps/backend/prisma/schema.prisma

@@ -18,12 +18,25 @@ model Scent {
 }
 
 model Category {
-  id        Int       @id @default(autoincrement())
-  name      String    @unique
-  imageUrl  String?
-  products  Product[]
-  createdAt DateTime  @default(now())
-  updatedAt DateTime  @updatedAt
+  id           Int                   @id @default(autoincrement())
+  name         String                @unique
+  imageUrl     String?
+  products     Product[]
+  translations CategoryTranslation[]
+  createdAt    DateTime              @default(now())
+  updatedAt    DateTime              @updatedAt
+}
+
+model CategoryTranslation {
+  id         Int      @id @default(autoincrement())
+  categoryId Int
+  category   Category @relation(fields: [categoryId], references: [id], onDelete: Cascade)
+  langCode   String
+  name       String
+  createdAt  DateTime @default(now())
+  updatedAt  DateTime @updatedAt
+
+  @@unique([categoryId, langCode])
 }
 
 model Product {