v0.8.0 — GetChunkPositions read RPC (chunk-position read-back)
Additive (minor): adds ChunkService.GetChunkPositions returning the calling
user's saved ChunkPosition{chunk_type, chunk_id, position} list (optional
chunk_type filter; identity server-derived). Completes the write/read pair with
v0.7.0's UpdateChunkPosition. Reuses ChunkType + HexPosition. No breaking changes.
Merged via !15 (register-chunk-position-read).