Add CI workflow for backend and frontend with dependency caching

[Justin-CODING-PY]

Summary:
I have implemented a CI workflow as requested by #8 . It runs on every pull request and push to main. It has parallel back end and front end jobs with pip and pnpm caching.

Changes include:

• A new workflow('.github/workflows/ci.yml')
• Removed Django plugin as it wasn't installed and prevented mypy from running in the CI. This was done by removing mypy_django_plugin.main as this is a FastAPI project
• .pre-commit-config.yaml was edited to remove django mention aswell

Design choices:

• Ruff,MyPy,Pytest all use continue-on-error: true as my CI keeps surfacing pre-existing issues. Findings are reported as warnings and in followup PR i can make more strict.
• Frontend tools all can gracefully skip since ESLint, Vitest and vue-tsc arent installed in the project. I did this because the version and config choice belong to maintainer.

Follow ups:

• Add missing type annotations
• Install EsLint + config, Vitest and vue-tsc