v0.42.0 — blockrun_video pays on Solana

blockrun_video now pays on Solana as well as Base. The Solana route uses
the gateway's payment-on-completion async flow: the job POST is issued once,
idempotent poll GETs tolerate transient disconnects, and their SVM transaction
is re-signed with a fresh blockhash every 20s so a slow Seedance 2.5 render can
settle at the end of a true 15-minute total budget (quote + submit + polling,
every request clamped to what is left). A gateway re-challenge is pinned to
the original amount, recipient and fee payer, and a payment signature is never
sent to a poll URL off the gateway's origin. A settle-failure 402 is read from
its PAYMENT-RESPONSE reason: a funding problem surfaces as one, while the
gateway's documented stale-blockhash re-sign path is bounded and, if
exhausted, reports the still-claimable job id instead of "out of funds". A
poll answer carrying a settlement receipt is booked before its body is
validated, so a truncated payload cannot erase a real charge from the ledger.

BLOCKRUN_KEYCHAIN=strict broke Solana image payments. blockrun_image
on Solana (and the new video route) loaded the wallet through the SDK's
file-only loader, which cannot see a key that strict mode has moved into the
OS keychain, so a funded wallet was reported as missing. Both now resolve the
key the same way blockrun_wallet does.