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>

pnpm-lock.yaml

@@ -93,6 +93,9 @@ importers:
       tailwindcss:
         specifier: ^4.2.4
         version: 4.2.4
+      tsx:
+        specifier: ^4.19.4
+        version: 4.21.0
       typescript:
         specifier: ^5.6.3
         version: 5.9.3