Add TransferTribe app and fix critical transfer security flaws

The application source was untracked, so this commit brings it under
version control together with fixes for the issues found while auditing
it. Notable fixes:

Authorization
- Require a session and scope to senderEmail on /api/transfers/[id]
  (GET, DELETE) and .../resend. These were unauthenticated over an
  autoincrement id, so the ids could be walked to soft-delete any
  transfer, read sender/recipient metadata, or make the app mail
  arbitrary recipients.
- Require a session on the legacy /api/send and /api/chunk-upload
  endpoints, and take the sender from the session rather than a request
  field so transfers cannot be posted as another user.

Encryption
- Replace the chunk encryption scheme. Every chunk was encrypted under
  one shared session IV with its auth tag discarded, which reuses the
  AES-GCM keystream (XORing two ciphertexts recovers plaintext without
  the key) and left the stored file undecryptable, surfacing to users as
  a wrong-password error. Chunks are now self-contained frames carrying
  their own random IV and auth tag, behind a magic+salt header.
- Files written by the previous format now report UNSUPPORTED_FORMAT
  instead of a misleading password error.

Download
- Verify the password against the stored bcrypt hash before serving a
  file, and enforce expiresAt and DELETED/EXPIRED status.
- Move the password from the query string into a POST body so it stays
  out of access logs and Referer headers.
- Record a download only after successful authentication.
- Decrypt frame by frame through a stream instead of buffering the whole
  file, and encode the Content-Disposition filename per RFC 5987.

Data exposure
- /api/download ran before the password prompt and returned the full
  transfer row, including absolute server file paths. It now returns
  only what the pre-password screen renders; filenames, message and
  recipient are withheld until /api/verify succeeds.

Correctness
- Fix BigInt handling that made /api/transfers and /api/transfers/[id]
  fail unconditionally (JSON.stringify cannot serialize BigInt, and
  seeding a BigInt reduce with 0 throws).
- Fail loudly on a missing chunk during reassembly rather than silently
  writing a corrupt file.
- Meter plan usage in plaintext bytes rather than on-disk encrypted size.

Ignore /uploads: it holds runtime transfer payloads, not source.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

prisma/schema.prisma

@@ -0,0 +1,110 @@
+// This is your Prisma schema file,
+// learn more about it in the docs: https://pris.ly/d/prisma-schema
+
+// Looking for ways to speed up your queries, or scale easily with your serverless or edge functions?
+// Try Prisma Accelerate: https://pris.ly/cli/accelerate-init
+
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "postgresql"
+  url      = env("DATABASE_URL")
+}
+
+enum TransferStatus {
+  ACTIVE
+  EXPIRED
+  DELETED
+}
+
+model User {
+  id            String   @id @default(cuid())
+  name          String?
+  email         String?  @unique
+  emailVerified DateTime?
+  image         String?
+  plan          String  @default("free") // "free", "rookie", or "pro"
+
+  // Optional
+  transfers     Transfer[] @relation("UserTransfers")
+  accounts      Account[]
+  sessions      Session[]
+}
+
+model Account {
+  id                String  @id @default(cuid())
+  userId            String
+  type              String
+  provider          String
+  providerAccountId String
+  refresh_token     String?
+  access_token      String?
+  expires_at        Int?
+  token_type        String?
+  scope             String?
+  id_token          String?
+  session_state     String?
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([provider, providerAccountId])
+}
+
+model Session {
+  id           String   @id @default(cuid())
+  sessionToken String   @unique
+  userId       String
+  expires      DateTime
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+}
+
+model VerificationToken {
+  identifier String
+  token      String   @unique
+  expires    DateTime
+
+  @@unique([identifier, token])
+}
+
+model Transfer {
+  id             Int      @id @default(autoincrement())
+  senderEmail    String
+  recipientEmail String
+  passwordHash   String?
+  downloadUrl    String   @unique
+  createdAt      DateTime @default(now())
+  expiresAt      DateTime
+  files          File[]
+  filenames      String? // JSON stringified array of filenames
+  totalFiles Int @default(0)  // new field to track number of files in transfer
+  totalSize      BigInt   @default(0) // Use BigInt to support files > 2GB
+  message    String?  // optional message
+  status         TransferStatus   @default(ACTIVE) // Added
+
+  userId         String? // Change from Int? to String?
+  user           User?   @relation("UserTransfers", fields: [userId], references: [id])
+}
+
+
+model File {
+  id         Int      @id @default(autoincrement())
+  name       String
+  path       String
+  size       BigInt   // Use BigInt to support files > 2GB
+  encryptionIv String? // 12-byte IV as base64 string for AES-GCM decryption
+  transferId Int
+  transfer   Transfer @relation(fields: [transferId], references: [id])
+  downloads  FileDownload[]   // New
+}
+
+model FileDownload {
+  id        Int      @id @default(autoincrement())
+  fileId    Int
+  file      File     @relation(fields: [fileId], references: [id], onDelete: Cascade)
+  timestamp DateTime @default(now())
+  ip        String?
+  userAgent String?
+}