[#320] Remove lib/viem.ts re-export shim

[realproject7]

Context

Audit #320 identified lib/viem.ts as a useless 1-line re-export shim that creates import path confusion (F1, F5). All 5 reviewers flagged it.

Task

lib/viem.ts contains only:

export { publicClient } from "./rpc";

Only one file imports from it: src/app/api/cron/backfill/route.ts:3. Everything else imports from lib/rpc.

Fix:

1. Update src/app/api/cron/backfill/route.ts — change import from "../../../../../lib/viem" to "../../../../../lib/rpc"
2. Delete lib/viem.ts

Acceptance Criteria

• lib/viem.ts deleted
• Backfill route imports publicClient from lib/rpc
• npm run build passes