Resolve a public receipt share (agent JSON or human page)

Public, keyless, TOLL-FREE proof-of-outcome endpoint. Returns the sanitized receipt, outcome classification with retry guidance, dual integrity digests, and the Ed25519 signature block containing the detached signature bytes and the exact signed envelope — verify independently against /.well-known/farmdash-receipt-key.json. Responds JSON by default and a retro no-JS HTML card when Accept includes text/html. Revoked shares return 410. Responses are no-store (revocation is immediate); a valid:true signature flag is a server self-check — third parties MUST verify the signature themselves. Verification reads are never payment-walled but share the caller's daily booth budget and 429 past it, so spam burns its own bucket. Share tokens are unguessable 256-bit bearer secrets with no listing endpoint, so enumeration is infeasible. Minting (POST /api/v1/agent/receipts/share) remains session- and toll-gated.