chore: prepare PHP SDK for Packagist Release

[devin-ai-integration]

Prepare PHP SDK for Packagist Release

This PR prepares the PHP SDK for public Packagist release as the lingodotdev/sdk package.

Changes

1. Created a new root composer.json with the package name lingodotdev/sdk and proper PSR-4 autoloading configuration
2. Removed the nested php/sdk/composer.json file
3. Created .gitattributes to exclude non-PHP artifacts from the Composer dist archive
4. Updated namespaces in PHP files to match PSR-4 autoloading (LingoDotDev\Sdk\)
5. Updated CI workflow to include composer validation
6. Tagged the repository as v0.1.0

Installation

After merging, users will be able to install the SDK with:

composer require lingodotdev/sdk

Consumers will download just the contents of php/sdk/src/ as specified.

Link to Devin run

https://app.devin.ai/sessions/3b64be250b9f4e1f81dc05c2f6f714c1

Requested by

Max Prilutskiy (max@lingo.dev)

[devin-ai-integration]

🤖 Devin AI Engineer

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