* fix: roll back document rows when FAISS insert fails
Validate embedding shape/dimension before local writes. If DocumentStorage
commits but FAISS write fails, best-effort delete the partial FAISS ids and
document rows so the two stores do not diverge.
* fix: clean up partial KB upload state before metadata commit
Track metadata_committed right after commit succeeds. On failure before
metadata commit, roll back chunks/vectors first, then residual KB rows and
media files. After metadata is committed, keep the document even if stats
or refresh fails.
* test: cover knowledge base upload atomicity and rollback
Add unit tests for insert_batch FAISS failure rollback, dimension validation
before document writes, upload cleanup order, no-rollback after metadata
commit, and real DocumentStorage+FAISS no-orphan cases.
* fix: log media directory cleanup failures after upload rollback
Best-effort rmdir of the per-document media directory should still emit a
warning when removal fails so incomplete cleanup is diagnosable.
296fcfb54a