Add new server SDKs to documentation

[goosewin]

Description

• Added documentation for the newly released PHP and Swift server SDKs.
• Integrated PHP and Swift SDKs into the navigation, the server SDKs overview page, and the web quickstart guide.
• Provided installation instructions and code examples for key functionalities (installation, assistant creation, bulk operations, webhook integration) for both PHP and Swift.

Testing Steps

• Run the app locally using fern docs dev or navigate to preview deployment
• Ensure that the changed pages and code snippets work

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Slack Thread

 

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
_{Learn more about Cursor Agents}

[github-actions]

🌿 Preview your docs: https://vapi-preview-f87287c5-e5be-4b40-8fb8-6e7062b14a9d.docs.buildwithfern.com