Plan — adk interactive TUI

This plan has been folded into the broader v4 overhaul.

See: adk-v4-overhaul.md — specifically §8 (TUI) and §12 (Extensibility plane).

The earlier draft of this document covered only the TUI in isolation. As the v4 scope expanded to cover GitHub-first migration, filesystem restructure, repo-layout overhaul, PR-task pr-review/ subfolder, skill rewiring, install/migration scripts, and TUI together, those concerns moved into a single coordinated plan. The TUI ships as Phase G of that plan.