Remove the legacy TUI split (#15922)

This is the part 1 of 2 PRs that will delete the `tui` /
`tui_app_server` split. This part simply deletes the existing `tui`
directory and marks the `tui_app_server` feature flag as removed. I left
the `tui_app_server` feature flag in place for now so its presence
doesn't result in an error. It is simply ignored.

Part 2 will rename the `tui_app_server` directory `tui`. I did this as
two parts to reduce visible code churn.

codex-rs/tui/tests/suite/no_panic_on_startup.rs

@@ -1,127 +0,0 @@
-use std::collections::HashMap;
-use std::path::Path;
-use std::time::Duration;
-use tokio::select;
-use tokio::time::timeout;
-
-/// Regression test for https://github.com/openai/codex/issues/8803.
-#[tokio::test]
-#[ignore = "TODO(mbolin): flaky"]
-async fn malformed_rules_should_not_panic() -> anyhow::Result<()> {
-    // run_codex_cli() does not work on Windows due to PTY limitations.
-    if cfg!(windows) {
-        return Ok(());
-    }
-
-    let tmp = tempfile::tempdir()?;
-    let codex_home = tmp.path();
-    std::fs::write(
-        codex_home.join("rules"),
-        "rules should be a directory not a file",
-    )?;
-
-    // TODO(mbolin): Figure out why using a temp dir as the cwd causes this test
-    // to hang.
-    let cwd = std::env::current_dir()?;
-    let config_contents = format!(
-        r#"
-# Pick a local provider so the CLI doesn't prompt for OpenAI auth in this test.
-model_provider = "ollama"
-
-[projects]
-"{cwd}" = {{ trust_level = "trusted" }}
-"#,
-        cwd = cwd.display()
-    );
-    std::fs::write(codex_home.join("config.toml"), config_contents)?;
-
-    let CodexCliOutput { exit_code, output } = run_codex_cli(codex_home, cwd).await?;
-    assert_ne!(0, exit_code, "Codex CLI should exit nonzero.");
-    assert!(
-        output.contains("ERROR: Failed to initialize codex:"),
-        "expected startup error in output, got: {output}"
-    );
-    assert!(
-        output.contains("failed to read rules files"),
-        "expected rules read error in output, got: {output}"
-    );
-    Ok(())
-}
-
-struct CodexCliOutput {
-    exit_code: i32,
-    output: String,
-}
-
-async fn run_codex_cli(
-    codex_home: impl AsRef<Path>,
-    cwd: impl AsRef<Path>,
-) -> anyhow::Result<CodexCliOutput> {
-    let codex_cli = codex_utils_cargo_bin::cargo_bin("codex")?;
-    let mut env = HashMap::new();
-    env.insert(
-        "CODEX_HOME".to_string(),
-        codex_home.as_ref().display().to_string(),
-    );
-
-    let args = vec!["-c".to_string(), "analytics.enabled=false".to_string()];
-    let spawned = codex_utils_pty::spawn_pty_process(
-        codex_cli.to_string_lossy().as_ref(),
-        &args,
-        cwd.as_ref(),
-        &env,
-        &None,
-        codex_utils_pty::TerminalSize::default(),
-    )
-    .await?;
-    let mut output = Vec::new();
-    let codex_utils_pty::SpawnedProcess {
-        session,
-        stdout_rx,
-        stderr_rx,
-        exit_rx,
-    } = spawned;
-    let mut output_rx = codex_utils_pty::combine_output_receivers(stdout_rx, stderr_rx);
-    let mut exit_rx = exit_rx;
-    let writer_tx = session.writer_sender();
-    let exit_code_result = timeout(Duration::from_secs(10), async {
-        // Read PTY output until the process exits while replying to cursor
-        // position queries so the TUI can initialize without a real terminal.
-        loop {
-            select! {
-                result = output_rx.recv() => match result {
-                    Ok(chunk) => {
-                        // The TUI asks for the cursor position via ESC[6n.
-                        // Respond with a valid position to unblock startup.
-                        if chunk.windows(4).any(|window| window == b"\x1b[6n") {
-                            let _ = writer_tx.send(b"\x1b[1;1R".to_vec()).await;
-                        }
-                        output.extend_from_slice(&chunk);
-                    }
-                    Err(tokio::sync::broadcast::error::RecvError::Closed) => break exit_rx.await,
-                    Err(tokio::sync::broadcast::error::RecvError::Lagged(_)) => {}
-                },
-                result = &mut exit_rx => break result,
-            }
-        }
-    })
-    .await;
-    let exit_code = match exit_code_result {
-        Ok(Ok(code)) => code,
-        Ok(Err(err)) => return Err(err.into()),
-        Err(_) => {
-            session.terminate();
-            anyhow::bail!("timed out waiting for codex CLI to exit");
-        }
-    };
-    // Drain any output that raced with the exit notification.
-    while let Ok(chunk) = output_rx.try_recv() {
-        output.extend_from_slice(&chunk);
-    }
-
-    let output = String::from_utf8_lossy(&output);
-    Ok(CodexCliOutput {
-        exit_code,
-        output: output.to_string(),
-    })
-}