feat(faiss): best-effort per-file embedding statuses

[greglum]

Summary

• embed each vector CSV independently so one bad document no longer fails the whole batch
• report a per-file SUCCESS/PARTIAL/FAILED entry in a new documentStatuses list, with inserted/failed/total record counts and an error message on failure
• roll a failed document back fully: its already-written per-Source artifacts are deleted and the in-memory vector state is restored, so no partially-indexed data survives under a FAILED label
• downgrade a document to PARTIAL or FAILED when post-write validation removes its artifacts, instead of silently shrinking createdDocuments
• build real per-file FileEmbeddingStatus entries in FaissDatabaseEngine from documentStatuses, keeping the previous index-level datasetsLoaded() check as a fallback when the response omits them

Why

#2205 made document embedding best-effort: every file is attempted and the reactor reports per-file FAILED/PARTIAL statuses. The FAISS engine bypasses that contract on its batched path — a single bad CSV raises out of Python and fails the entire batch, and when the batch completes the engine stamps every file SUCCESS or every file FAILED from one index-level boolean. Separately, artifacts that fail validation after writing are removed from createdDocuments without any signal to the caller. This PR extends the #2205 contract to FAISS.

Behavior change

Per-file embedding failures in the FAISS batch path now return FAILED statuses instead of raising — the same deliberate shift #2205 made for the documents path. Batch-level guards ahead of the loop are unchanged and still raise.

Depends on

Builds on #2759 (its first commit); only the top commit here is new. Review #2759 first.

Verification

• 12 Python unit tests pass (7 new in test_faiss_best_effort_status.py; 5 in test_faiss_batch_vector_csv.py, of which one was updated because it asserted the old fail-fast behavior)
• mvn compile succeeds on the full project
• Black clean on changed files; Ruff reports only the six pre-existing diagnostics in faiss_client.py

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.