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/src/test_support.rs

@@ -0,0 +1,28 @@
+use codex_utils_absolute_path::AbsolutePathBuf;
+use std::path::Path;
+use std::path::PathBuf;
+
+pub(crate) trait PathExt {
+    fn abs(&self) -> AbsolutePathBuf;
+}
+
+impl PathExt for Path {
+    fn abs(&self) -> AbsolutePathBuf {
+        AbsolutePathBuf::try_from(self.to_path_buf())
+            .unwrap_or_else(|_| panic!("path should already be absolute"))
+    }
+}
+
+pub(crate) trait PathBufExt {
+    fn abs(&self) -> AbsolutePathBuf;
+}
+
+impl PathBufExt for PathBuf {
+    fn abs(&self) -> AbsolutePathBuf {
+        self.as_path().abs()
+    }
+}
+
+pub(crate) fn test_path_display(path: &str) -> String {
+    Path::new(path).abs().display().to_string()
+}