Remove buffer mode feature and relocate cache metrics

- Remove buffer mode toggle (Normal/Large/Huge) as demuxer settings
  do not significantly impact local file playback
- Move cache duration metric from title bar to bottom status bar
- Display cache alongside codec, bitrate, and sample rate info
- Remove 'b' key binding and Buffer context menu option
- Update version to 0.1.15

src/main.rs

@@ -348,7 +348,7 @@ async fn handle_key_event<B: ratatui::backend::Backend>(terminal: &mut Terminal<
                 let max_items = match menu.menu_type {
                     ContextMenuType::FilePanel => 2,
                     ContextMenuType::Playlist => 2,
-                    ContextMenuType::TitleBar => 3,
+                    ContextMenuType::TitleBar => 4,
                 };
                 if menu.selected_index < max_items - 1 {
                     menu.selected_index += 1;
@@ -700,7 +700,7 @@ fn handle_mouse_event(state: &mut AppState, mouse: MouseEvent, title_bar_area: r
         let items = match menu.menu_type {
             ContextMenuType::FilePanel => 2,
             ContextMenuType::Playlist => 2,
-            ContextMenuType::TitleBar => 3,
+            ContextMenuType::TitleBar => 4,
         };
         let popup_width = 13;
         let popup_height = items as u16 + 2; // +2 for borders