fix: implement Composer Path Repository for PHP SDK publishing

[devin-ai-integration]

Fix PHP SDK Packagist publishing with Composer Path Repository

Issue

The PHP packagist publishing workflow was failing because Packagist requires composer.json to be at the repository root, but our PHP SDK is in a subdirectory (php/sdk/).

Fix

Implemented the Composer Path Repository approach:

• Created a root composer.json file that references the PHP SDK in the subdirectory
• Configured a path repository pointing to the PHP SDK directory
• Updated the workflow to install dependencies from the root composer.json
• Added version validation to ensure the PHP SDK always has a valid version

How It Works

1. The root composer.json defines a path repository that points to the php/sdk directory
2. When Packagist scans the repository, it finds the composer.json at the root
3. The workflow installs dependencies from the root, which creates a vendor directory with the PHP SDK
4. The version is still managed in the PHP SDK's composer.json for proper versioning

Testing

The fix should be verified when the workflow runs on the next push to main that affects the PHP SDK.

Link to Devin run: https://app.devin.ai/sessions/b645cd58d26f45afb714a736ec4d758e
User: Max Prilutskiy (max@lingo.dev)

[devin-ai-integration]

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