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`.

docs/development.md

@@ -18,9 +18,9 @@ You could run other types of tests as well, but they may take longer time and ov
 
 - Run unit tests: `npm run test:unit`
 - Run integration tests: `npm run test:integration`
-- Run e2e (end-to-end) tests
-  - Interactive mode with GUI: `npm run test:e2e`
-  - Headless mode without GUI: `npm run test:e2e -- --headless`
+- Run end-to-end (e2e) tests:
+  - `npm run test:cy:open`: Run tests interactively using the development server with hot-reloading.
+  - `npm run test:cy:run`: Run tests on the production build in a headless mode.
 
 📖 Read more about testing in [tests](./tests.md).