Move TUI on top of app server (parallel code) (#14717)

This PR replicates the `tui` code directory and creates a temporary
parallel `tui_app_server` directory. It also implements a new feature
flag `tui_app_server` to select between the two tui implementations.

Once the new app-server-based TUI is stabilized, we'll delete the old
`tui` directory and feature flag.

codex-rs/tui_app_server/src/skills_helpers.rs

@@ -0,0 +1,43 @@
+use codex_core::skills::model::SkillMetadata;
+use codex_utils_fuzzy_match::fuzzy_match;
+
+use crate::text_formatting::truncate_text;
+
+pub(crate) const SKILL_NAME_TRUNCATE_LEN: usize = 21;
+
+pub(crate) fn skill_display_name(skill: &SkillMetadata) -> &str {
+    skill
+        .interface
+        .as_ref()
+        .and_then(|interface| interface.display_name.as_deref())
+        .unwrap_or(&skill.name)
+}
+
+pub(crate) fn skill_description(skill: &SkillMetadata) -> &str {
+    skill
+        .interface
+        .as_ref()
+        .and_then(|interface| interface.short_description.as_deref())
+        .or(skill.short_description.as_deref())
+        .unwrap_or(&skill.description)
+}
+
+pub(crate) fn truncate_skill_name(name: &str) -> String {
+    truncate_text(name, SKILL_NAME_TRUNCATE_LEN)
+}
+
+pub(crate) fn match_skill(
+    filter: &str,
+    display_name: &str,
+    skill_name: &str,
+) -> Option<(Option<Vec<usize>>, i32)> {
+    if let Some((indices, score)) = fuzzy_match(display_name, filter) {
+        return Some((Some(indices), score));
+    }
+    if display_name != skill_name
+        && let Some((_indices, score)) = fuzzy_match(skill_name, filter)
+    {
+        return Some((None, score));
+    }
+    None
+}