Switch from SuperTokens to NextAuth.js

BREAKING CHANGE: Replace SuperTokens with NextAuth.js

Why:
- SuperTokens had persistent Traefik routing issues
- SSL certificate not issuing correctly
- Complex infrastructure (separate container)
- NextAuth runs in Next.js app (simpler, no separate service)

Changes:
- Install next-auth, @auth/prisma-adapter, prisma
- Create NextAuth API route: app/api/auth/[...nextauth]/route.ts
- Add Prisma schema for NextAuth tables (users, sessions, accounts)
- Update auth page to use NextAuth signIn()
- Remove all SuperTokens code and dependencies
- Keep same Google OAuth (just simpler integration)

Benefits:
- No separate auth service needed
- No Traefik routing issues
- Sessions stored in Montreal PostgreSQL
- Simpler configuration
- Battle-tested, widely used

All authentication data stays in Montreal!

Co-authored-by: Cursor <cursoragent@cursor.com>

prisma/schema.prisma

@@ -0,0 +1,62 @@
+// Prisma schema for NextAuth.js
+// This defines the database tables for authentication
+
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "postgresql"
+  url      = env("DATABASE_URL")
+}
+
+model Account {
+  id                String  @id @default(cuid())
+  userId            String  @map("user_id")
+  type              String
+  provider          String
+  providerAccountId String  @map("provider_account_id")
+  refresh_token     String? @db.Text
+  access_token      String? @db.Text
+  expires_at        Int?
+  token_type        String?
+  scope             String?
+  id_token          String? @db.Text
+  session_state     String?
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([provider, providerAccountId])
+  @@map("accounts")
+}
+
+model Session {
+  id           String   @id @default(cuid())
+  sessionToken String   @unique @map("session_token")
+  userId       String   @map("user_id")
+  expires      DateTime
+  user         User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@map("sessions")
+}
+
+model User {
+  id            String    @id @default(cuid())
+  name          String?
+  email         String?   @unique
+  emailVerified DateTime? @map("email_verified")
+  image         String?
+  accounts      Account[]
+  sessions      Session[]
+
+  @@map("users")
+}
+
+model VerificationToken {
+  identifier String
+  token      String   @unique
+  expires    DateTime
+
+  @@unique([identifier, token])
+  @@map("verification_tokens")
+}