refactor: extract interactive model setup for reuse by coder setup

Extract the radioSelect-based interactive model setup flow into a
reusable runInteractiveModelSetup() function, shared by both --model
and --setup. The coder setup wizard now reuses the full TUI-like
provider/model selection instead of simplistic readline prompts,
and automatically launches the coder TUI after setup completes.

Co-Authored-By: DeepSeek <noreply@deepseek.com>

Author: jimgqyu