- Flyway V13: add file_hash column to documents and document_annotations
- FileService.uploadFile() now returns UploadResult(s3Key, fileHash) with SHA-256 hash computed from raw bytes
- Document and DocumentAnnotation models gain a fileHash field
- DocumentService propagates the hash at all three upload sites (storeDocument, createDocument, updateDocument)
- AnnotationService.createAnnotation() accepts and persists a fileHash
- AnnotationController resolves the document's hash and passes it through
Closes#55
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>