m11p1 — decoupled ack/ship path: staged writes (seqno+WAL+relay-push,
microseconds) separate from group-commit fsync; ShipQueue batches+windows
outbound segments; receiver coalesces inbound chunks before applying.
Adds first tidaldb_cluster_* metrics.
m11p2 — leader WAL is now THE replicated log: fsynced batches feed a
bounded WalShipFeed and ship byte-identical to followers; WAL seqnos
survive restarts (relay-reset hazard gone). Item metadata and embeddings
journal kind-1/2 blob records on the same stream as signals; the m8p10
HTTP broadcast is deleted. StreamSegments catch-up is follower-pulled via
server-streaming RPC, triggered on gap detection, follower boot, and
leader heal nudge. Promote carries a stream baseline so peers skip
pre-stream history.
