v2: Cloud feature parity audit for collection fork and indexing status

[oss-amikos]

Context\nchroma-go cloud suite includes coverage for cloud-specific features such as collection fork and indexing status.\n\n## Scope\n- Audit Java v2 support status for collection fork and indexing status APIs.\n- Implement missing functionality where appropriate, or explicitly document as unsupported.\n- Add tests/docs for whichever path is chosen.\n\n## Acceptance Criteria\n- Feature support status is explicit and tested/documented.\n- No ambiguous parity state remains for these cloud-specific capabilities.\n\nRelated: #94