Let seam /status resolve a reservation by pair

[anderdc]

Companion to the ventura-labs-allways-app red-team round (2026-08-26). Validator seam only.

Failure mode

/status without a swap_key walks the miner's per-hub reservation slots and answers with the freshest one. A consumer tracking one seat (the app) has no way to ask for its slot, so a stranger reserved on the miner's other hub was read as "another user holds this miner" — the app refunded a seat that had just been finalized for its user and left the reservation live and untracked — and a same-pubkey stranger there (a declared SOL address is not proof of ownership) was adopted as the consumer's own reservation.

/status now takes optional from_chain/to_chain and returns the slot carrying that pair (none if no such slot), unchanged behaviour without them. The read cache keys on the pair too.

Checks: ruff clean; pytest tests/ 2033 pass — the 3 test_bitcoin_signing failures are order-dependent and present on test already (they pass in isolation).