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

src/app/api/signup/route.ts

@@ -0,0 +1,40 @@
+import { NextResponse } from "next/server";
+import bcrypt from "bcryptjs";
+import { z } from "zod";
+import { prisma } from "@/lib/prisma";
+
+const signupSchema = z.object({
+  name: z.string().trim().min(1, "Name is required").max(80),
+  email: z.string().trim().toLowerCase().email("Enter a valid email"),
+  password: z.string().min(8, "Password must be at least 8 characters"),
+  age: z.number().int().min(18, "You must be 18 or older to join").max(120),
+});
+
+export async function POST(request: Request) {
+  const body = await request.json().catch(() => null);
+  if (!body) {
+    return NextResponse.json({ error: "Invalid request body" }, { status: 400 });
+  }
+
+  const parsed = signupSchema.safeParse(body);
+  if (!parsed.success) {
+    const message = parsed.error.issues[0]?.message ?? "Invalid input";
+    return NextResponse.json({ error: message }, { status: 400 });
+  }
+
+  const { name, email, password, age } = parsed.data;
+
+  const existing = await prisma.user.findUnique({ where: { email } });
+  if (existing) {
+    return NextResponse.json({ error: "An account with that email already exists" }, { status: 409 });
+  }
+
+  const passwordHash = await bcrypt.hash(password, 12);
+
+  const user = await prisma.user.create({
+    data: { name, email, age, passwordHash },
+    select: { id: true, email: true, name: true },
+  });
+
+  return NextResponse.json({ user }, { status: 201 });
+}