docs(xet): document v2 CAS API + batch reconstruction; fix xorb chunk limit
Addresses drift found by the xet-docs-refresh audit against xetcas@3c753ea
and xet-core@v1.5.1:
- api.md: add the /v2 endpoints and batch reconstruction, which the client
actively uses but were undocumented — GET /v2/reconstructions/{file_id},
GET /v2/file-chunk-hashes/{file_id}, POST /v1/reconstructions (batch), and
the streaming POST /v2/shards.
- xorb.md: correct "no explicit limit on the number of chunks" — source
enforces MAX_XORB_CHUNKS = 8192 in addition to the 64 MiB serialized cap.
Ref huggingface-internal/xetcas#1175, huggingface-internal/xetcas#1176
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wr4cVEYeGC1kGZ9mVidzxP