chore(deps): update pydantic requirement from >=2.7 to >=2.13.4

Updates the requirements on [pydantic](https://github.com/pydantic/pydantic) to permit the latest version.
- [Release notes](https://github.com/pydantic/pydantic/releases)
- [Changelog](https://github.com/pydantic/pydantic/blob/main/HISTORY.md)
- [Commits](pydantic/pydantic@v2.7.0...v2.13.4)

---
updated-dependencies:
- dependency-name: pydantic
  dependency-version: 2.13.4
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

api/requirements.txt

@@ -2,7 +2,7 @@ fastapi>=0.140.7
 uvicorn[standard]>=0.51.0
 psycopg2-binary>=2.9
 python-multipart>=0.0.9
-pydantic>=2.7
+pydantic>=2.13.4
 # BUG-032: schema migrations for csv_uploads.* — auto-runs at API startup
 # via alembic upgrade head (see api/db.py bootstrap and alembic/ directory).
 alembic>=1.13.0