Use dynamic port assignment for manual test CI.

[przemyslaw-zan]

🚀 Summary

check-manual-tests.sh now discovers a free port via a Node.js one-liner (binding to port 0), passes it to the server with --port, and forwards it to the web crawler through pnpm run manual:verify --port. The web crawler resolves the port from the --port CLI argument or falls back to 8125. This prevents CI failures when port 8125 is already in use.

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📌 Related issues

• Closes https://github.com/ckeditor/ckeditor5-internal/issues/4352.

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[martnpaneq]

I think that using .port file is not the best solution, as it could be confusing when using two repositories. On the other hand I don't see any better solution.

After some local testing, we keep two instances of the .port file, depending on the repository where the script was invoked. It is too confusing, and I think we should go with reading the port number from the cli instead.

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[martnpaneq]

The changes look much better after implementing the new approach.