Feature/remove ResponseAnnotations model

[gecBurton]

Context

The ResponseAnnotation model was a 1:1 relationship with Response, acting as a thin wrapper with no independent lifecycle. Flattening it into Response simplifies queries, reduces joins, removes the need to manage annotation creation separately from responses, and makes the data model more intuitive.

Changes proposed in this pull request

• Removes the ResponseAnnotation model and consolidates all annotation fields (sentiment, evidence_rich, human_reviewed, reviewed_by, reviewed_at, flagged_by, themes) directly onto the Response model
• Migrates ResponseAnnotationTheme through-table to reference Response directly instead of ResponseAnnotation
• Adds history tracking (django-simple-history) to Response itself
• Updates all dependent code (serializers, views, filters, services, export, data pipeline sync, admin, factories, tests) to reference fields on Response rather than via response.annotation.*

Migrations

Four sequential migrations handle the data migration safely:

• 0094: Adds response FK to ResponseAnnotationTheme; back-populates from response_annotation.response
• 0095: Adds HistoricalResponse, moves themes M2M to Response, removes old response_annotation FK from through-table
• 0096: Adds annotation fields (sentiment, evidence_rich, human_reviewed, etc.) to Response; back-populates from existing ResponseAnnotation records
• 0097: Drops ResponseAnnotation and HistoricalResponseAnnotation models entirely

Guidance to review

Link to Trello ticket

https://incubatorforartificialintelligence.atlassian.net/wiki/spaces/Consult/pages/25559057/Tech+Debt#Add-ResponseAnnotation.is_edited-field

Things to check

• I have added any new ENV vars in all deployed environments and updated the .env.test files in the repo