feat: email+password auth with db-backed sessions

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/(auth)/signup/page.tsx

@@ -0,0 +1,12 @@
+import { signUp } from "@/lib/actions";
+import { AuthForm } from "@/components/auth-form";
+export default function Signup() {
+  return <>
+    <h1 style={{ fontFamily: "var(--qai-font-display)", fontSize: "var(--qai-text-2xl)" }}>Create account</h1>
+    <AuthForm action={signUp} submit="Create account" fields={[
+      { name: "email", label: "Email", type: "email", autoComplete: "email" },
+      { name: "password", label: "Password", type: "password", autoComplete: "new-password",
+        help: "10 characters minimum." }]} />
+    <p><a href="/login">Sign in instead</a></p>
+  </>;
+}