docs(iocraft): add interactive render loop design document

Added comprehensive design document for implementing interactive TUI
capabilities in Socket CLI using iocraft's full render loop API.

The document outlines:
- Current state: static rendering only (renderToString)
- Target state: interactive components with hooks, events, state
- Architecture: render loop, component model, event handling
- Implementation plan: phased approach with milestones
- API design: functional component factory pattern
- Risk analysis and mitigation strategies

This is planning documentation for future interactive TUI features
such as Button, TextInput, real-time progress indicators, and
interactive configuration wizards.

Author: jdalton