feat: add Plivo SMS admin panel with rate limits

backend/prisma/schema.prisma

@@ -18,12 +18,15 @@ model User {
   totalEarned   Int      @default(0) @map("total_earned")
   totalSpent    Int      @default(0) @map("total_spent")
   watchTimeMinutes Int   @default(0) @map("watch_time_minutes")
+  phoneNumber   String?  @map("phone_number")
+  smsOptOut     Boolean  @default(false) @map("sms_opt_out")
 
   transactions     Transaction[]
   watchEvents      WatchEvent[]
   contentRequests  ContentRequest[]
   sessions         Session[]
   kofiPayments     KofiPayment[]
+  smsLogs          SmsLog[]
 
   createdAt DateTime @default(now()) @map("created_at")
   updatedAt DateTime @updatedAt @map("updated_at")
@@ -140,6 +143,22 @@ model KofiPayment {
   @@map("kofi_payments")
 }
 
+model SmsLog {
+  id          String   @id @default(uuid())
+  userId      String?  @map("user_id")
+  user        User?    @relation(fields: [userId], references: [id])
+  phoneNumber String   @map("phone_number")
+  message     String
+  status      String   @default("SENT")
+  plivoUuid   String?  @map("plivo_uuid")
+  error       String?
+  sentAt      DateTime @default(now()) @map("sent_at")
+
+  @@index([userId])
+  @@index([sentAt])
+  @@map("sms_logs")
+}
+
 enum TransactionType {
   EARN
   SPEND