docs(sdks): Restructure SDK docs and prune legacy integrations

[Arcapas]

Summary

This PR reorganizes the SDK documentation and prunes all legacy/out-of-scope integration references (Lite, Headless, Seamless, Direct API, React Native) to prepare the content for migration to Mintlify. It focuses exclusively on Full Checkout and Secure Fields.

Changes:

• Restructuring: Reorganized all platform-specific guides into docs/SDKs/Full Checkout/ and docs/SDKs/Card Enrollment/.
• Legacy Pruning: Excised all references to "Lite", "Headless", "Seamless", and "Direct API" integration modes.
• Platform Cleanup: Removed the React Native quickstart guide.
• Reference Updates: Audited and standardized web.md, ios.md, and android.md common references.
• Workspace Cleanup: Deleted the legacy Yuno SDKs directory from the core repository.
• Global Sidebar: Updated the root _order.yaml to reflect the new structure.

Key Pages:

• SDK Overview
• Full Checkout (Web)
• Card Enrollment (Web)