fix(auth): remove self-referential pages.signIn config

pages.signIn is meant to point at a CUSTOM sign-in page. Setting it to
'/api/auth/signin' — Auth.js's own built-in endpoint — makes Auth.js
redirect there whenever it wants the sign-in page, which is the same
endpoint, producing ERR_TOO_MANY_REDIRECTS in browsers.

Omitting the setting falls back to Auth.js's default sign-in handler,
which renders the provider-picker HTML at /api/auth/signin instead of
redirecting.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/auth.ts

@@ -21,8 +21,9 @@ export const { auth, handlers, signIn, signOut } = NextAuth({
   ],
   secret: env().NEXTAUTH_SECRET,
   session: { strategy: "jwt" },
-  // Sign-in page is the default Auth.js form; can be customized later.
+  // No custom `pages.signIn`: Auth.js serves its default provider-picker UI
-  pages: { signIn: "/api/auth/signin" },
+  // at /api/auth/signin. Setting it to that exact path causes a redirect
+  // loop because Auth.js redirects to the configured page → which is itself.
   callbacks: {
     async jwt({ token, account, profile }) {
       // On first call after sign-in, `account` + `profile` are populated.