fix: stop setup tui crashes in bunx

[anand-testcompare]

Summary

• remove the OpenTUI tree shape that was producing orphan text nodes during sandcode setup
• disable OpenTUI mouse capture in setup so normal terminal text selection works
• keep the setup wizard behavior otherwise unchanged

Testing

• bun run check
• bun run typecheck
• bun test
• bun run build
• interactive bun src/sandcode.ts setup smoke in a TTY