docs: fold the known issue into the create_index bullet

It sat under '### Added', which read as 'Added: Known issue'. Folding it
in keeps the Keep a Changelog headings meaning what they say, and 'as of
this release' stops the present tense going stale once the engine ships
a fix.

Author: rohan-hotdata

CHANGELOG.md

@@ -17,9 +17,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   in the CLI. The build is a background job whose submit call reports success even
   when the build later fails, so this polls the job and raises `RuntimeError` with
   its error message; `wait=False` returns as soon as the job is accepted. Returns
-  `CreateIndexResult`, also exported.
-- Known issue: a vector index is not yet used by the query planner on a managed
-  database. Reproduces via the CLI, so it is engine-side; BM25 is unaffected.
+  `CreateIndexResult`, also exported. Note that as of this release the query planner
+  does not use a vector index on a managed database, so those queries stay correct
+  but unaccelerated; this is engine-side (it reproduces via the CLI) and BM25 is
+  unaffected.
 
 ## [0.9.0] - 2026-07-23