Refactor and improve external URL checks

- Move external URL checks to its own module under `tests/`. This
  separates them from integration test, addressing long runs and
  frequent failures that led to ignoring test results.
- Move `check-desktop-runtime-errors` to `tests/checks` to keep all
  test-related checks into one directory.
- Replace `ts-node` with `vite` for running
  `check-desktop-runtime-errors` to maintain a consistent execution
  environment across checks.
- Implement a timeout for each fetch call.
- Be nice to external sources, wait 5 seconds before sending another
  request to an URL under same domain. This solves rate-limiting issues.
- Instead of running test on every push/pull request, run them only
  weekly.
- Do not run tests on each commit/PR but only scheduled (weekly) to
  minimize noise.
- Fix URLs are not captured correctly inside backticks or parenthesis.

docs/development.md

@@ -21,7 +21,10 @@ You could run other types of tests as well, but they may take longer time and ov
 - 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.
-- Run runtime checks for packaged desktop applications: `npm run check:desktop`, see its [README.md](./../scripts/check-desktop-runtime-errors/README.md).
+- Run checks:
+  - `npm run check:desktop`: Run runtime checks for packaged desktop applications ([README.md](./../tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/README.md)).
+    - You can set environment variables active its flags such as `BUILD=true SCREENSHOT=true npm run check:desktop`
+  - `npm run check:external-urls`: Test whether external URLs used in applications are alive.
 
 📖 Read more about testing in [tests](./tests.md).