Live compression fixture #

live.dict is the 65,536-byte decoded v2 dictionary from the sibling archive server's src/assets/zstd_dictionary_v2.b64 (server base revision 1765e48). The loopback rotation test changes only the dictionary ID in a copy to model replacement. It emits independently framed zstd raw blocks with that ID; actual compressed blocks are exercised by atproto-bench's generated corpus.