🐛 | Code quality fixes

- config.py: move 'import shutil' to module level
- player.py: unify type hints, narrow except, add debug log
- discord_rpc.py: replace broad except Exception with specific types
- gui.py: remove unused import; replace lambda closures with method refs; fix closure scope bug; extract _populate_list_page() to remove duplicate code; add public accessors; make flush_volume public; add AudioVisualizer.reset_activity()
- tests: replace unused _f variable with Path.touch()

player.py

@@ -39,6 +39,9 @@ import shutil
 import threading
 from typing import Optional
 
+# In this module we use Optional[str] for consistency
+# with Qt signal/slot typing conventions.
+
 import yt_dlp
 
 # ═══════════════════════════════════════════════════════════════════════════
@@ -75,7 +78,7 @@ VERBOSE:   bool = False    # enable yt-dlp debug output
 # Temp-file housekeeping
 # ═══════════════════════════════════════════════════════════════════════════════
 
-_TUNETTI_TMP: str | None = None
+_TUNETTI_TMP: Optional[str] = None
 
 
 def _tmp_dir() -> str:
@@ -166,6 +169,8 @@ class DownloadWorker(QObject):
     @Slot(int, dict)
     def _do_download(self, task_id: int, song: dict) -> None:
         """Entry point — invoked on the worker thread."""
+        log.debug("Download starting: task_id=%d, video_id=%s",
+                   task_id, song.get("videoId") or song.get("video_id", ""))
         self._task_id = task_id
         self._cancelled = False
 
@@ -232,7 +237,7 @@ class DownloadWorker(QObject):
                 if not self._cancelled:
                     self.download_succeeded.emit(task_id, resolved)
 
-        except Exception as exc:
+        except (OSError, RuntimeError) as exc:
             log.error("Download error for %s: %s", video_id, exc)
             self._cleanup_path(temp_path)
             with self._lock: