Add household seeding & session (task 07)

- scripts/seed.ts: idempotent pnpm db:seed inserts "Home" household if none exists (powered by tsx)
- signIn callback: first member of household gets owner role, subsequent users get member
- src/lib/session.ts: getCurrentSession() returns { user, household, role }, throws if unauthenticated or unmembered
- /settings/household: member list for all roles; rename form gated to owner only (server action also enforces)

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

src/lib/auth.ts

@@ -41,8 +41,6 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
   callbacks: {
     async signIn({ user }) {
       if (!user.id) return true;
-      // Attach user to the single household if not already a member.
-      // (Household is seeded by task 07; this is a no-op until then.)
       const existing = await db
         .select()
         .from(householdMembers)
@@ -51,9 +49,15 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
       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 })
+            .values({ householdId: household.id, userId: user.id, role })
             .onConflictDoNothing();
         }
       }