tui: remove debug/test-only crate features (#16457)

## Why

The remaining `vt100-tests` and `debug-logs` features in `codex-tui`
were only gating test-only and debug-only behavior. Those feature
toggles add Cargo and Bazel permutations without buying anything, and
they make it easier for more crate features to linger in the workspace.

## What changed

- delete `vt100-tests` and `debug-logs` from `codex-tui`
- always compile the VT100 integration tests in the TUI test target
instead of hiding them behind a Cargo feature
- remove the unused textarea debug logging branch instead of replacing
it with another gate
- add the required argument-comment annotations in the VT100 tests now
that Bazel sees those callsites during linting
- shrink the manifest verifier allowlist again so only the remaining
real feature exceptions stay permitted

## How tested

- `cargo test -p codex-tui`
- `just argument-comment-lint -p codex-tui`

codex-rs/tui/tests/all.rs

@@ -1,6 +1,5 @@
 // Single integration test binary that aggregates all test modules.
 // The submodules live in `tests/suite/`.
-#[cfg(feature = "vt100-tests")]
 mod test_backend;
 
 #[allow(unused_imports)]