Queue device commands and replay first results

The router parses each delivery once and keeps singles and ordered
batches in one bounded queue per device. Expiry, ownership, and caller
cancellation limit intake and queue backpressure. The device consumer
checks physical access and expiry again before work.

A shared per-device ledger retains the first 256 results with stable
metadata. Duplicate requests replay that result after uncertain delivery
without another action. Insertion order bounds memory, and callers
cannot mutate stored timestamps. The command and framework documents
state the signal behavior and the memory-only safety limits.

Issue: 40b314f