Make PHP v6 client constructible after production install

[iFixRobots]

I installed the new PHP v6 release into a clean Composer project and found that installation succeeded, but constructing BeeperDesktop\Client failed:

Next Http\Discovery\Exception\NotFoundException: No PSR-17 url factory found. Install a package from this list: https://packagist.org/providers/psr/http-factory-implementation

src/Client.php:98-104 asks discovery for a URI, stream, request factory, and HTTP client. composer.json only required the PSR interfaces; its concrete Guzzle implementation was under require-dev, which consumers do not install. I moved Guzzle to require and updated the lockfile so an ordinary production install supplies the client and factories. In a fresh --no-dev install, new Client(...) now succeeds and exposes LabelsService. I bumped the version to 6.0.1 rather than changing the already published v6.0.0 tag.

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