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>

package.json

@@ -18,6 +18,7 @@
     "typecheck": "tsc --noEmit",
     "db:generate": "drizzle-kit generate",
     "db:migrate": "drizzle-kit migrate",
+    "db:seed": "tsx --env-file=.env scripts/seed.ts",
     "db:studio": "drizzle-kit studio"
   },
   "devDependencies": {
@@ -34,6 +35,7 @@
     "prettier": "^3.3.3",
     "tailwindcss": "^4.2.4",
     "typescript": "^5.6.3",
+    "tsx": "^4.19.4",
     "typescript-eslint": "^8.15.0"
   },
   "dependencies": {