Add external URL linting for markdown files

This commit integrates `remark-lint-no-dead-urls` into the project's
linting process, improving documentation quality by checking for dead
links.

Key changes:

- Add NPM command to verify external URLs in markdown files
- Include new command in the main lint script

Other supporting changes:

- Replace archive.ph link with Wayback Machine for better verification
- Update `remark-lint-no-dead-urls` to latest version (2.0.0)
- Update Browserslist DB to latest to avoid build errors

.github/workflows/checks.quality.yaml

@@ -11,8 +11,9 @@ jobs:
           - npm run lint:eslint
           - npm run lint:yaml
           - npm run lint:md
-          - npm run lint:md:relative-urls
           - npm run lint:md:consistency
+          - npm run lint:md:relative-urls
+          - npm run lint:md:external-urls
         os: [ macos, ubuntu, windows ]
       fail-fast: false # Still interested to see results from other combinations
     steps: