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/session.ts

@@ -0,0 +1,31 @@
+import { eq } from "drizzle-orm";
+import { auth } from "@/lib/auth";
+import { db } from "@/lib/db";
+import { householdMembers, households, users } from "@/modules/_core/schema";
+
+export interface CurrentSession {
+  user: typeof users.$inferSelect;
+  household: typeof households.$inferSelect;
+  role: "owner" | "member";
+}
+
+export async function getCurrentSession(): Promise<CurrentSession> {
+  const session = await auth();
+  if (!session?.user?.id) throw new Error("Not authenticated");
+
+  const [row] = await db
+    .select({
+      user: users,
+      household: households,
+      role: householdMembers.role,
+    })
+    .from(householdMembers)
+    .innerJoin(users, eq(householdMembers.userId, users.id))
+    .innerJoin(households, eq(householdMembers.householdId, households.id))
+    .where(eq(householdMembers.userId, session.user.id))
+    .limit(1);
+
+  if (!row) throw new Error("No household membership");
+
+  return row;
+}