feat(pos): implement integrated full-screen POS point-of-sale system with inventory deduction and thermal receipt

apps/backend/src/routes/customers.ts

@@ -66,4 +66,34 @@ export const customersRoute = new Elysia({ prefix: "/customers" })
       pointsDelta: t.Number(),
       reason: t.Optional(t.String())
     })
+  })
+  .post("/", async ({ body, set }) => {
+    try {
+      const { displayName, phone, email } = body as { displayName?: string, phone?: string, email?: string };
+      
+      // Auto-generate a unique lineUserId placeholder for in-store/POS customers
+      const lineUserId = `POS_${Date.now()}_${Math.random().toString(36).substring(2, 8)}`;
+      
+      const newCustomer = await prisma.customer.create({
+        data: {
+          lineUserId,
+          displayName: displayName || "ลูกค้าหน้าร้าน",
+          phone: phone || null,
+          email: email || null,
+          points: 0
+        }
+      });
+      return newCustomer;
+    } catch (err: any) {
+      console.error("[Customers] Create error:", err);
+      set.status = 400;
+      return { error: err.message || "Failed to create customer" };
+    }
+  }, {
+    body: t.Object({
+      displayName: t.Optional(t.String()),
+      phone: t.Optional(t.String()),
+      email: t.Optional(t.String())
+    })
   });
+