Close the last open items on #743 before merge:
- Conformance: document two isolation arms (cross-id for all backends;
same-id/different-namespace for supports_namespace_isolation advertisers).
- No silent drop: non-advertising backends must raise UnsupportedCapabilityError
when PalaceRef.namespace is set, rather than accept-and-ignore.
- Wire require_namespace_support() into chroma/sqlite_exact; add conformance test.
- Refresh implementation-status banner now that #1727/#1731/#1732/#1734 landed.
Igor Lins e Silva
aeac794c1a