DTS API documentation

[sunt05]

Parent Epic

Part of #1045 (Epic: DTS Accessor Interface - Eliminate df_state Intermediate Layer)

Summary

Create comprehensive documentation for the DTS API and migration guide for users.

Depends On

• DTS core infrastructure with single-grid runner and SUEWSSimulation integration #1072 (DTS core infrastructure)

Scope

• API reference for DTS module
• User guide for backend="dts" usage
• Migration guide from traditional path
• Example notebooks demonstrating DTS workflow
• Performance considerations and best practices

Deliverables

• API reference in Sphinx docs
• "Using DTS Backend" user guide
• Migration guide for existing users
• Example notebook(s)
• FAQ section