feat: annotation caption for s3 and db/api ingestion

[surygeng]

Summary

• Adds AnnotationCaption as a new annotation shape type, enabling per-instance text captions tied to a companion annotation shape (e.g., InstanceSegmentation, Point)
• Uses saber for annotation format
• Follows the same pattern as GlobalCaption, but with a companion_shape parameter that disambiguates filenames when multiple shapes exist in the same annotation directory (e.g., membrane-1.0_instancesegmentation_caption.json)
• Updates schema definitions, S3 ingestion, DB/API schema, and codegen

Tests

All unit tests passed

[PALLAVIKHEDLE]

🚀 LGTM, thanks!