Add Jest for frontend testing

[zhoukerrr]

What feature(s) would you like to see in RepoSense

Currently, Cypress is the only tool for frontend testing. While it is an excellent choice for end-to-end tests, it is not ideal for unit tests. Using Cypress for unit tests will take up too much time. By adding Jest, we will be able to catch more regression bugs quickly.

We will also need to add code coverage for jest tests and integrate with the CI.

[sopa301]

I suggest we use Vitest instead because vue-cli is being put on maintenance and its suggested replacement create-vue runs on Vite.