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/src/markdown.rs

@@ -1,116 +0,0 @@
-use ratatui::text::Line;
-use std::path::Path;
-
-/// Render markdown into `lines` while resolving local file-link display relative to `cwd`.
-///
-/// Callers that already know the session working directory should pass it here so streamed and
-/// non-streamed rendering show the same relative path text even if the process cwd differs.
-pub(crate) fn append_markdown(
-    markdown_source: &str,
-    width: Option<usize>,
-    cwd: Option<&Path>,
-    lines: &mut Vec<Line<'static>>,
-) {
-    let rendered = crate::markdown_render::render_markdown_text_with_width_and_cwd(
-        markdown_source,
-        width,
-        cwd,
-    );
-    crate::render::line_utils::push_owned_lines(&rendered.lines, lines);
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use pretty_assertions::assert_eq;
-    use ratatui::text::Line;
-
-    fn lines_to_strings(lines: &[Line<'static>]) -> Vec<String> {
-        lines
-            .iter()
-            .map(|l| {
-                l.spans
-                    .iter()
-                    .map(|s| s.content.clone())
-                    .collect::<String>()
-            })
-            .collect()
-    }
-
-    #[test]
-    fn citations_render_as_plain_text() {
-        let src = "Before 【F:/x.rs†L1】\nAfter 【F:/x.rs†L3】\n";
-        let mut out = Vec::new();
-        append_markdown(src, None, None, &mut out);
-        let rendered = lines_to_strings(&out);
-        assert_eq!(
-            rendered,
-            vec![
-                "Before 【F:/x.rs†L1】".to_string(),
-                "After 【F:/x.rs†L3】".to_string()
-            ]
-        );
-    }
-
-    #[test]
-    fn indented_code_blocks_preserve_leading_whitespace() {
-        // Basic sanity: indented code with surrounding blank lines should produce the indented line.
-        let src = "Before\n\n    code 1\n\nAfter\n";
-        let mut out = Vec::new();
-        append_markdown(src, None, None, &mut out);
-        let lines = lines_to_strings(&out);
-        assert_eq!(lines, vec!["Before", "", "    code 1", "", "After"]);
-    }
-
-    #[test]
-    fn append_markdown_preserves_full_text_line() {
-        let src = "Hi! How can I help with codex-rs today? Want me to explore the repo, run tests, or work on a specific change?\n";
-        let mut out = Vec::new();
-        append_markdown(src, None, None, &mut out);
-        assert_eq!(
-            out.len(),
-            1,
-            "expected a single rendered line for plain text"
-        );
-        let rendered: String = out
-            .iter()
-            .flat_map(|l| l.spans.iter())
-            .map(|s| s.content.clone())
-            .collect::<Vec<_>>()
-            .join("");
-        assert_eq!(
-            rendered,
-            "Hi! How can I help with codex-rs today? Want me to explore the repo, run tests, or work on a specific change?"
-        );
-    }
-
-    #[test]
-    fn append_markdown_matches_tui_markdown_for_ordered_item() {
-        let mut out = Vec::new();
-        append_markdown("1. Tight item\n", None, None, &mut out);
-        let lines = lines_to_strings(&out);
-        assert_eq!(lines, vec!["1. Tight item".to_string()]);
-    }
-
-    #[test]
-    fn append_markdown_keeps_ordered_list_line_unsplit_in_context() {
-        let src = "Loose vs. tight list items:\n1. Tight item\n";
-        let mut out = Vec::new();
-        append_markdown(src, None, None, &mut out);
-
-        let lines = lines_to_strings(&out);
-
-        // Expect to find the ordered list line rendered as a single line,
-        // not split into a marker-only line followed by the text.
-        assert!(
-            lines.iter().any(|s| s == "1. Tight item"),
-            "expected '1. Tight item' rendered as a single line; got: {lines:?}"
-        );
-        assert!(
-            !lines
-                .windows(2)
-                .any(|w| w[0].trim_end() == "1." && w[1] == "Tight item"),
-            "did not expect a split into ['1.', 'Tight item']; got: {lines:?}"
-        );
-    }
-}