test(config): migrate TUI config tests to Effect runner

[kitlangton]

Summary

• Migrates test/config/tui.test.ts to the Effect-native test runner via it.instance.
• Replaces Promise-style temp/global/env cleanup with scoped Effect resource helpers and AppFileSystem operations.
• Removes direct Effect.runPromise, AppRuntime, and provideTestInstance usage from the migrated test file.

Verification

• bun run test test/config/tui.test.ts
• bun typecheck

Notes

• bun install initially failed while building tree-sitter-powershell, but enough dependencies were present afterward for test and typecheck to pass.