feat: scope sample similarity search to project

Commit notes

- Add projectId option to SimilaritySearchOptions interface - Update findSimilarSamples to filter by project ID - Update findSimilarSamplesFallback fallback function similarly - When projectId not provided, inherit from source sample's project - Add project_id query parameter to /library/samples/:id/similar endpoint

Co-authored-by: armin.naimi <[email redacted]>