chore: cleanup unused down migrations and tests in the backend folder

[themarolt]

Summary

Removes obsolete down-migration SQL files, a 10k-line dead webhook events test fixture, and a couple of stale backend config artifacts. Pure cleanup — no runtime behavior changes. Shrinks the repo, drops dead deps, and trims noise from migration listings.

Changes

• Deleted ~290 U*__*.sql down-migration files from backend/src/database/migrations/ and services/libs/database/src/product/migrations/. Down migrations aren't part of the rollout path here, so they were dead weight.
• Removed backend/src/serverless/integrations/webhooks/__tests__/events.ts (10,585 lines of fixture data no longer referenced).
• Dropped backend/babel.config.json (TS toolchain no longer goes through Babel).
• Pruned 6 lines from backend/package.json (devDeps tied to the removed Babel/test setup).
• Minor scripts/cli tweak and resulting pnpm-lock.yaml regeneration.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Performance improvement
• Chore / dependency update
• Documentation

---

Note

Low Risk
Low risk cleanup that mainly deletes unused SQL down-migration files and removes unreferenced dev tooling; the main risk is only to local rollback/testing workflows that may still rely on the deleted artifacts.

Overview
Removes a large set of unused U*__*.sql down-migration files from backend/src/database/migrations (and a leftover product down migration), reducing migration noise and repo size.

Drops legacy backend tooling/config by deleting backend/babel.config.json, removing the test script, and pruning related devDependencies (Babel presets/core plus supertest/node-mocks-http) from backend/package.json.

^{Reviewed by Cursor Bugbot for commit a400003. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Copilot]

Copilot wasn't able to review this pull request because it exceeds the maximum number of files (300). Try reducing the number of changed files and requesting a review from Copilot again.

[github-actions]

⚠️ Jira Issue Key Missing

Your PR title doesn't contain a Jira issue key. Consider adding it for better traceability.

Example:

• feat: add user authentication (CM-123)
• feat: add user authentication (IN-123)

Projects:

• CM: Community Data Platform
• IN: Insights

Please add a Jira issue key to your PR title.