[Platform][Higgsfield] Add platform bridge

[OskarStark]

Q	A
Bug fix?	no
New feature?	yes
Docs?	no
Issues	-
License	MIT

This adds a new symfony/ai-higgsfield-platform bridge integrating Higgsfield, an AI creative suite for image and video generation. Because Higgsfield works asynchronously, the client submits a generation request, polls the status endpoint until the media is ready, downloads it and returns it as a BinaryResult (so ->asFile() works as with other media bridges). The model name maps directly to a Higgsfield generation endpoint (e.g. flux-pro/kontext/max/text-to-image, v1/image2video/dop), and an ImageNormalizer maps Image inputs to Higgsfield's image_url shape. The bridge ships with a Factory, ModelCatalog, contract, unit tests, and runnable examples under examples/higgsfield/.

$platform = Factory::createPlatform(apiKey: 'KEY_ID', apiSecret: 'KEY_SECRET');
$result = $platform->invoke(
    'flux-pro/kontext/max/text-to-image',
    new Text('A cat on a kitchen table'),
    [
        'aspect_ratio' => '9:16'
    ],
);
$result->asFile('cat.png');