Add playlist bounds validation and search mode visual indicator

- Add bounds checking to prevent accessing invalid playlist indices
- Yellow/orange selection bar when in search mode
- Validate playlist index after navigation operations
- Handle empty playlists gracefully

src/state/mod.rs

@@ -271,6 +271,10 @@ impl AppState {
             if let Some(first) = self.playlist.first() {
                 self.current_file = Some(first.clone());
                 self.player_state = PlayerState::Playing;
+            } else {
+                // Empty playlist
+                self.current_file = None;
+                self.player_state = PlayerState::Stopped;
             }
         } else if let Some(item) = self.get_selected_item() {
             let node = item.node.clone();
@@ -281,6 +285,10 @@ impl AppState {
                 if let Some(first) = self.playlist.first() {
                     self.current_file = Some(first.clone());
                     self.player_state = PlayerState::Playing;
+                } else {
+                    // Empty directory
+                    self.current_file = None;
+                    self.player_state = PlayerState::Stopped;
                 }
             } else {
                 // Play single file
@@ -296,8 +304,11 @@ impl AppState {
     pub fn play_next(&mut self) {
         if self.playlist_index + 1 < self.playlist.len() {
             self.playlist_index += 1;
-            self.current_file = Some(self.playlist[self.playlist_index].clone());
-            self.player_state = PlayerState::Playing;
+            // Double-check index is valid before accessing
+            if self.playlist_index < self.playlist.len() {
+                self.current_file = Some(self.playlist[self.playlist_index].clone());
+                self.player_state = PlayerState::Playing;
+            }
         }
     }