chore(deps): bump mypy from 1.19.1 to 2.0.0 in /backend

Bumps [mypy](https://github.com/python/mypy) from 1.19.1 to 2.0.0.
- [Changelog](https://github.com/python/mypy/blob/master/CHANGELOG.md)
- [Commits](python/mypy@v1.19.1...v2.0.0)

---
updated-dependencies:
- dependency-name: mypy
  dependency-version: 2.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/requirements-dev.txt

@@ -1,6 +1,6 @@
 # Development and CI/CD Dependencies
 ruff==0.15.12
-mypy==1.19.1
+mypy==2.0.0
 pytest==9.0.3
 pytest-asyncio==1.3.0
 httpx==0.28.1