Add Phase 0: sign-up, login, and profile

- Next.js (App Router) + TypeScript + Tailwind
- Prisma + SQLite for the User model
- Sign-up with 18+ age gate, email/password validation (zod), bcrypt hashing
- Login via NextAuth credentials provider, JWT sessions
- Protected /profile route (view + edit name/bio)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VL5YUEf2B9LG4xdVUQwcSg

prisma/schema.prisma

@@ -0,0 +1,19 @@
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "sqlite"
+  url      = env("DATABASE_URL")
+}
+
+model User {
+  id           String   @id @default(cuid())
+  email        String   @unique
+  passwordHash String
+  name         String
+  age          Int
+  bio          String   @default("")
+  createdAt    DateTime @default(now())
+  updatedAt    DateTime @updatedAt
+}