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/app/settings/household/actions.ts

@@ -0,0 +1,22 @@
+"use server";
+
+import { eq } from "drizzle-orm";
+import { revalidatePath } from "next/cache";
+import { db } from "@/lib/db";
+import { getCurrentSession } from "@/lib/session";
+import { households } from "@/modules/_core/schema";
+
+export async function renameHousehold(formData: FormData) {
+  const { household, role } = await getCurrentSession();
+  if (role !== "owner") throw new Error("Forbidden");
+
+  const name = formData.get("name");
+  if (typeof name !== "string" || !name.trim()) throw new Error("Invalid name");
+
+  await db
+    .update(households)
+    .set({ name: name.trim() })
+    .where(eq(households.id, household.id));
+
+  revalidatePath("/settings/household");
+}