lokahi: sequencer mode

Enable kona's sequencer per chain in lokahi config; conductor + the direct sequencer-to-gossip edge compose unchanged; message filtering stays EL-side (op-interop-filter). No reliance on publish-after-insert gossip ordering (gossip-before-insert is a known future optimization). Gate: acceptance — one sequencing chain, one follower, cross-safe advances.

Depends on: #22532 (N-chain service). Parallel to phases 3–4.

🤖 *Co-created with Claude (Fable 5)*

Start by reading dependency #22532 and the lokahi configuration and service components it introduces. Trace how kona sequencing, the conductor, and the direct sequencer-to-gossip edge are wired, then verify the acceptance case: one sequencing chain, one follower, and cross-safe advances without relying on publish-after-insert ordering.

Written by the indexing model from the issue text.