Vercel edge function that watches Solana's Memo program for nt1: memos and
indexes them in Upstash KV. The ZKSend wallet polls this endpoint instead of
doing full client-side scans.
GET /api/recent?since=<slot>&limit=200 → JSON array of memo entries.
vercel devRequires UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN.
The mirror is read-only public data. ECDH still happens locally in the wallet — the mirror never sees recipient identities.