[codex] Fix index and document ingestion reliability

[WERvEX]

Summary

• Scope index freshness checks by shared/private identity instead of blocking an entire workspace.
• Serialize document retry, deletion, and worker claims; add 409 conflicts and Qdrant compensation cleanup.
• Validate chat, embedding, and HuggingFace provider endpoints consistently.
• Fix frontend index rebuild targeting and clear Ruff findings.

Validation

• pytest -q: 50 passed
• npm test -- --run: 7 passed
• npm run build: passed
• ruff check .: passed
• ruff format --check .: passed

Notes

No database migration or new infrastructure was introduced. Real Qdrant/model services were not started; integration-sensitive paths are covered with mocks in the test suite.