Remove signIn callback — enrollment now happens in getCurrentSession

Auth.js v5 calls signIn before the new user's row is fully committed, so
inserting into household_members immediately caused a FK violation for any
new user (e.g. cam on first sign-in). Enrollment is now handled lazily in
getCurrentSession's auto-enroll fallback, which runs after the session is
established and the user row is guaranteed to exist.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/auth.ts

@@ -3,15 +3,10 @@ import NextAuth, { type DefaultSession } from "next-auth";
 import { db } from "@/lib/db";
 import {
   accounts,
-  households,
-  householdMembers,
   sessions,
   users,
   verificationTokens,
 } from "@/modules/_core/schema";
-import { eq } from "drizzle-orm";
-import { ensureDefaultCalendarsForMembership } from "@/modules/calendar/server/defaults";
-import { ensureDefaultListsForHousehold } from "@/modules/lists/server/defaults";
 
 declare module "next-auth" {
   interface Session {
@@ -41,35 +36,6 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
     signIn: "/login",
   },
   callbacks: {
-    async signIn({ user }) {
-      if (!user.id) return true;
-      const existing = await db
-        .select()
-        .from(householdMembers)
-        .where(eq(householdMembers.userId, user.id))
-        .limit(1);
-      if (existing.length === 0) {
-        const [household] = await db.select().from(households).limit(1);
-        if (household) {
-          const [anyMember] = await db
-            .select()
-            .from(householdMembers)
-            .where(eq(householdMembers.householdId, household.id))
-            .limit(1);
-          const role = anyMember ? "member" : "owner";
-          await db
-            .insert(householdMembers)
-            .values({ householdId: household.id, userId: user.id, role })
-            .onConflictDoNothing();
-          await ensureDefaultCalendarsForMembership({
-            householdId: household.id,
-            userId: user.id,
-          });
-          await ensureDefaultListsForHousehold(household.id);
-        }
-      }
-      return true;
-    },
     session({ session, user }) {
       session.user.id = user.id;
       return session;