fix CLOUD-219
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **Bug Fixes**
- Ensured that documents without content now receive a placeholder embedding, improving consistency in document processing.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
fix AI-20
fix AI-77
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Enhanced relevance-based re-ranking for embedding results, improving the accuracy of content suggestions.
- Added prioritization for workspace content that matches specific document IDs in search results.
- Introduced a new scoped threshold parameter to refine workspace document matching.
- **Improvements**
- Increased default similarity threshold for file chunk matching, resulting in more precise matches.
- Doubled candidate retrieval for file and workspace chunk matching to improve result quality.
- Updated sorting to prioritize context-relevant documents in workspace matches.
- Explicitly included original input content in re-ranking calls for better relevance assessment.
- **Bug Fixes**
- Adjusted re-ranking logic to return only highly relevant results based on confidence scores.
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