Reverse image search (paid, agent rail)

Phash-based reverse image search over the approved catalog. PAID endpoint (agent payment rails — no account needed; the payment is the auth). Attach proof via PAYMENT-SIGNATURE or X-PAYMENT header (base64 JSON x402 payload, USDC on Base) or Authorization: L402 <macaroon>:<preimage> (Lightning sats). Without proof the response is 402 with a dual-rail offer. Rate limited 30/min/IP. Returns 404 while payments are disabled. Price: $0.02 per call (paid in sats over Lightning at the current BTC/USD rate, or in USDC on Base). Same SSRF hardening and input rules as /v1/images/reverse-search.