feat: download tracks with full ID3 metadata

- Add downloads.py: "Artist - Title.mp3" naming, no-overwrite dedupe,
  configurable download_dir, progress and per-item callbacks.
- Save maximum metadata via tags.py (ID3v2.3, mutagen): artists, album
  and album artist, track/disc, year/date, raw genre, label, duration,
  explicit flag, cover 600x600, plain and synced lyrics (MTS then
  LRCLIB), track URLs and Yandex/MTS ids.
- TUI/Qt: download current track and queue from the menu, "d" key in
  lists, folder picker in settings; CLI download gains -d/--dir and
  --no-tags.
- Add mutagen to requirements and document download/metadata in README.
- Fix MPRIS update_metadata crashing without dbus-next.

qt_app.py

@@ -44,6 +44,7 @@ from PySide6.QtWidgets import (
     QAbstractButton,
     QCheckBox,
     QComboBox,
+    QFileDialog,
     QFrame,
     QHBoxLayout,
     QLabel,
@@ -313,6 +314,53 @@ class Task(QRunnable):
             pass
 
 
+class DownloadTask(QRunnable):
+    """Скачивает список треков в фоне и сообщает о прогрессе."""
+
+    class Signals(QObject):
+        progress = Signal(str)
+        done = Signal(int, int, str)
+        failed = Signal(str)
+
+    def __init__(self, api, tracks: list[dict], dest: str) -> None:
+        super().__init__()
+        self.api = api
+        self.tracks = tracks
+        self.dest = dest
+        self.signals = DownloadTask.Signals()
+        self.setAutoDelete(False)
+
+    def run(self) -> None:
+        from downloads import download_many
+
+        def on_item(index: int, count: int, track: dict) -> None:
+            title = str(track.get("title") or "")
+            self._emit(f"Скачиваю {index}/{count}: {title}")
+
+        try:
+            saved = download_many(
+                self.api, self.tracks, self.dest, on_item=on_item)
+        except Exception as exc:  # noqa: BLE001 - сообщение показываем в UI
+            self._emit_failed(str(exc) or exc.__class__.__name__)
+        else:
+            try:
+                self.signals.done.emit(len(saved), len(self.tracks), self.dest)
+            except RuntimeError:
+                pass
+
+    def _emit(self, text: str) -> None:
+        try:
+            self.signals.progress.emit(text)
+        except RuntimeError:
+            pass
+
+    def _emit_failed(self, message: str) -> None:
+        try:
+            self.signals.failed.emit(message)
+        except RuntimeError:
+            pass
+
+
 class CoverView(QWidget):
     """Обложка со скруглениями и аккуратным плейсхолдером."""
 
@@ -569,6 +617,7 @@ class QtMusicApp(QMainWindow):
         self.pool = QThreadPool(self)
         self.pool.setMaxThreadCount(4)
         self.covers = QNetworkAccessManager(self)
+        self._download_tasks: set[DownloadTask] = set()
 
         self.player = QMediaPlayer(self)
         self.audio = QAudioOutput(self)
@@ -1006,6 +1055,22 @@ class QtMusicApp(QMainWindow):
         self.wave_check.toggled.connect(self.on_wave_from_history_toggled)
         layout.addWidget(self.wave_check)
 
+        dir_row = QHBoxLayout()
+        dir_row.setSpacing(10)
+        dir_label = QLabel("Папка загрузок")
+        dir_label.setObjectName("settingLabel")
+        self.download_dir_edit = QLineEdit(
+            str(self.settings.get("download_dir") or ""))
+        self.download_dir_edit.setObjectName("settingCombo")
+        self.download_dir_edit.setReadOnly(True)
+        dir_button = QPushButton("Выбрать…")
+        dir_button.setCursor(Qt.CursorShape.PointingHandCursor)
+        dir_button.clicked.connect(self.choose_download_dir)
+        dir_row.addWidget(dir_label)
+        dir_row.addWidget(self.download_dir_edit, 1)
+        dir_row.addWidget(dir_button)
+        layout.addLayout(dir_row)
+
         hint = QLabel("Настройки сохраняются в .mts-music/settings.json")
         hint.setObjectName("pageStatus")
         hint.setWordWrap(True)
@@ -1043,6 +1108,62 @@ class QtMusicApp(QMainWindow):
     def on_wave_from_history_toggled(self, checked: bool) -> None:
         self.update_setting("wave_from_history", checked)
 
+    def choose_download_dir(self) -> None:
+        current = str(self.settings.get("download_dir") or "")
+        chosen = QFileDialog.getExistingDirectory(
+            self, "Папка загрузок", current)
+        if not chosen:
+            return
+        self.update_setting("download_dir", chosen)
+        self.download_dir_edit.setText(chosen)
+        self.toast(f"Папка загрузок: {chosen}")
+
+    # -- скачивание -------------------------------------------------------
+
+    def download_current(self) -> None:
+        self.close_drawer()
+        if not self.current:
+            self.toast("Сначала выбери трек")
+            return
+        self.download_tracks([self.current], "трек")
+
+    def download_queue(self) -> None:
+        self.close_drawer()
+        tracks = self.queue or ([self.current] if self.current else [])
+        if not tracks:
+            self.toast("Список пуст")
+            return
+        self.download_tracks(tracks, "список")
+
+    def download_tracks(self, tracks: list[dict], label: str) -> None:
+        if not tracks:
+            return
+        dest = str(self.settings.get("download_dir") or "")
+        task = DownloadTask(self.api, list(tracks), dest)
+        task.signals.progress.connect(self.set_top_status)
+        task.signals.done.connect(
+            lambda saved, total, folder, t=task:
+            self._download_done(t, saved, total, folder))
+        task.signals.failed.connect(
+            lambda message, t=task: self._download_failed(t, message))
+        self._download_tasks.add(task)
+        self.set_top_status(f"Скачиваю {label}…")
+        self.pool.start(task)
+
+    def _download_done(
+        self, task: DownloadTask, saved: int, total: int, dest: str
+    ) -> None:
+        self._download_tasks.discard(task)
+        self.set_top_status(self.queue_name)
+        if saved:
+            self.toast(f"Скачано {saved}/{total} → {dest}")
+        else:
+            self.toast("Не удалось скачать")
+
+    def _download_failed(self, task: DownloadTask, message: str) -> None:
+        self._download_tasks.discard(task)
+        self.on_error(message)
+
     def show_settings(self) -> None:
         self._show(self.settings_page)
 
@@ -1071,6 +1192,8 @@ class QtMusicApp(QMainWindow):
             ("История", self.show_history),
             ("Поиск", self.show_search),
             ("Текст песни", self.show_lyrics),
+            ("Скачать трек", self.download_current),
+            ("Скачать список", self.download_queue),
             ("Настройки", self.show_settings),
         ):
             button = QPushButton(text)