feat(cms): implement multi-language support across frontend and admin UI

apps/backend/src/routes/menus.ts

@@ -102,4 +102,44 @@ export const menusRoute = new Elysia({ prefix: "/menus" })
         order: t.Number()
       }))
     })
+  })
+  .patch("/items/:id/translations", async ({ params, body, set }) => {
+    const id = Number(params.id);
+    if (isNaN(id)) {
+      set.status = 400;
+      return { error: "Invalid menu item ID" };
+    }
+
+    const payload = body as any;
+    const results: any[] = [];
+    const LANGS = ['th', 'en', 'ja', 'zh', 'vi', 'ko'];
+
+    for (const lang of LANGS) {
+      const label = typeof payload.label === 'string' ? (lang === 'th' ? payload.label : null) : payload.label?.[lang];
+      if (!label) continue;
+
+      const existing = await prisma.menuItemTranslation.findUnique({
+        where: { menuItemId_langCode: { menuItemId: id, langCode: lang } }
+      });
+
+      if (existing) {
+        const updated = await prisma.menuItemTranslation.update({
+          where: { id: existing.id },
+          data: { label }
+        });
+        results.push(updated);
+      } else {
+        const created = await prisma.menuItemTranslation.create({
+          data: { menuItemId: id, langCode: lang, label }
+        });
+        results.push(created);
+      }
+    }
+
+    const updated = await prisma.menuItem.findUnique({
+      where: { id },
+      include: { translations: true }
+    });
+
+    return { success: true, translations: results, menuItem: updated };
   });