v0.7.0 — generic ChunkService + UpdateChunkPosition (chunk_type enum)

BREAKING (pre-1.0 minor): replaces ClusterService with a generic ChunkService;
adds UpdateChunkPosition(ChunkType chunk_type, string chunk_id, HexPosition);
removes UpdateClusterPosition + Cluster.position (field 8 reserved). ChunkType
is a code-shipped enum (CHUNK_TYPE_UNSPECIFIED=0, CHUNK_TYPE_CLUSTER=1).
Cluster/ListClusters/GetCluster unchanged. Regenerated Go + TS. Merged via !14
(register-generic-chunk-position).