Migrate Cypress (E2E) tests to Vite and TypeScript

This commit progresses the migration from Vue CLI to Vite (#230).

TypeScript migration:

- Convert JavaScript Cypress tests and configurations to TypeScript.
- Introduce `tsconfig.json` for Cypress, following official
  recommendation.

Test execution:

- Use Cypress CLI to run the tests.
- Rename Cypress commands to reflect official naming conventions.
- Start Vue server prior to Cypress execution, using
  `start-server-and-test` package based on official documentation.
- Remove dependency on Vue CLI plugin ((`@vue/cli-plugin-e2e-cypress`).

Configuration standardization (based on Cypress docs):

- Delete unused `plugins/` directory.
- Move test (spec) files to to the root directory.
- Add official ESLint plugin (`eslint-plugin-cypress`).

Changes for importing `vite.config.ts` into `cypress.config.ts`:

- Add TypeScript import assertations to files importing JSON files.
- Use ESM friendly way instead of `__dirname` to solve `ReferenceError:
  __dirname is not defined in ES module scrope`.

Other changes:

- Simplify comments in placeholder files.
- Create Cypress specific `.gitignore` for enhanced maintainability,
  clarity and scalability.
- Remove redundant `vue.config.cjs`.

.github/workflows/tests.e2e.yaml

@@ -23,4 +23,4 @@ jobs:
         run: npm ci
       -
         name: Run e2e tests
-        run: npm run test:e2e -- --headless
+        run: npm run test:cy:run