Consolidate documentation/reports with coverage

Currently, there is a dedicated `backend/docs` folder for project documentation, but I would like a consolidated docs folder that includes any relevant documentation *anywhere in the system*. We need to do the following

- [x] Move `backend/docs` to a `docs` folder in the root directory
- [ ] Consolidate coverage analysis that commits a single html report to the `docs` folder:
- [ ] The coverage analysis should run on Actions whenever a PR is created *OR* when there is a merge into main. However, the report should only be committed (and badge in `README.md` updated) when it is accepted into main.
- [x] Both backend and frontend coverage should be analyzed in a single report (not as separate scripts/tools, if it can be avoided)
- [x] Only typescript files that are in our repo (i.e. no libraries or third-party dependencies) should be analyzed