Release v0.15.2 - xchain-node

[jdogresorg]

Patch release: the pinned component set moves the hub, the explorer and the sync client to 0.15.2. The other nine components keep the tags they shipped under.

• xchain-hub 0.15.2: the hourly ATTEST response batch anchors on the BTC tip the attestation poll observed when no chain tip was pushed to the hub, so a validator without its own Bitcoin indexer can lead and co-sign batches.
• xchain-explorer 0.15.2: the custom-content frame on a token page stops growing without bound, and its media is allowed to load.
• xchain-sync 0.15.2: a replica repairs a lookup-table hole below its cursor, and the append-only events log is left out of the table-count comparison.

The manifest was written by the release manifest generator from the tagged state of every component; each of the three moved tags is signed by the platform release key and reachable from that repository master.