W38: Selected file count badge in border title

Append a '● N marked' badge to the active panel's border title
when files are selected, using the accent colour for visibility.
Makes the selection count visible even when the footer row is
hidden (e.g. on very short panels).

Tests: 1400 pass, zero warnings.

local/recipes/tui/tlc/source/src/filemanager/render.rs

@@ -306,7 +306,16 @@ impl FileManager {
                     format!("  {}% free", pct)
                 },
             );
-            format!(" {} {space} ", format_utils::path_short(panel.path()))
+            // Append a "N marked" badge if files are selected.
+            let marked = if panel.marked_count() > 0 {
+                format!("  ● {} marked", panel.marked_count())
+            } else {
+                String::new()
+            };
+            format!(
+                " {} {space} {marked} ",
+                format_utils::path_short(panel.path())
+            )
         } else {
             format!(" {} ", format_utils::path_short(panel.path()))
         };