Rename tui_app_server to tui (#16104)

This is a follow-up to https://github.com/openai/codex/pull/15922. That
previous PR deleted the old `tui` directory and left the new
`tui_app_server` directory in place. This PR renames `tui_app_server` to
`tui` and fixes up all references.

codex-rs/tui/tests/all.rs

@@ -0,0 +1,9 @@
+// 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)]
+use codex_cli as _; // Keep dev-dep for cargo-shear; tests spawn the codex binary.
+
+mod suite;