Remove expand/collapse markers from UI

- Clean display with only directory names and / suffix
- No [+] or [-] markers shown
- Directories still expand/collapse with h/l
- Minimal vifm-style appearance

src/ui/mod.rs

@@ -24,13 +24,8 @@ fn render_file_panel(frame: &mut Frame, state: &AppState, area: Rect) {
         .enumerate()
         .map(|(idx, item)| {
             let indent = "  ".repeat(item.depth);
-            let expand_marker = if item.node.is_dir {
-                if item.is_expanded { "[-] " } else { "[+] " }
-            } else {
-                "    "
-            };
             let suffix = if item.node.is_dir { "/" } else { "" };
-            let text = format!("{}{}{}{}", indent, expand_marker, item.node.name, suffix);
+            let text = format!("{}{}{}", indent, item.node.name, suffix);
 
             let style = if idx == state.selected_index {
                 Style::default().fg(Color::Black).bg(Color::Cyan)