The 64-entry per-chunk palette was a wire-format artifact and capped a chunk
at 64 distinct tiles. A Chunk is now Box<[u16; 1024]> with flags derived from
the id on lookup — the same layout a binary on-disk format would use.
Map path becomes the first CLI argument; assets/map_large is a generated
256×256 stress map (loads in ~0.5 ms release). The snapshot test takes
SNAPSHOT_MAP.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
