UI/UX polish: Tools menu, clickable timeline, live drag-seek, drag-and-drop load

- Clap detection moved from inline buttons to a Tools menu, plain labels
  (no more '(whole file)' / '(from cursor)' parentheticals) -- status
  messages moved to the window's status bar since the dedicated label
  widget went away with the button row.
- ClickableSlider subclass: clicking anywhere along the seek track jumps
  straight there instead of QSlider's default page-by-a-step behavior;
  reposition-then-delegate-to-super keeps native drag behavior intact.
- Dragging now seeks live via sliderMoved instead of waiting for
  sliderReleased.
- PlayerWidget accepts drag-and-drop of a local file to load it.

Verified with real Qt events (QMouseEvent clicks, a QDropEvent, a real
mouse click via xdotool opening the Tools menu on an actual running
window) rather than just calling the underlying methods directly.

player_widget.py

@@ -9,7 +9,7 @@ import time
 
 import mpv
 from PyQt6.QtWidgets import QWidget
-from PyQt6.QtCore import Qt
+from PyQt6.QtCore import Qt, pyqtSignal
 
 
 class PlayerWidget(QWidget):
@@ -20,10 +20,13 @@ class PlayerWidget(QWidget):
     this exists instead of a QMediaPlayer/HTML5-video-style backend.
     """
 
+    fileDropped = pyqtSignal(str)
+
     def __init__(self, parent=None):
         super().__init__(parent)
         self.setAttribute(Qt.WidgetAttribute.WA_DontCreateNativeAncestors)
         self.setAttribute(Qt.WidgetAttribute.WA_NativeWindow)
+        self.setAcceptDrops(True)
 
         # QApplication resets LC_NUMERIC to the system locale on construction,
         # which undoes python-mpv's own import-time fix and makes libmpv abort
@@ -108,3 +111,14 @@ class PlayerWidget(QWidget):
 
     def shutdown(self):
         self.mpv.terminate()
+
+    def dragEnterEvent(self, event):
+        if event.mimeData().hasUrls() and any(u.isLocalFile() for u in event.mimeData().urls()):
+            event.acceptProposedAction()
+
+    def dropEvent(self, event):
+        for url in event.mimeData().urls():
+            if url.isLocalFile():
+                self.fileDropped.emit(url.toLocalFile())
+                event.acceptProposedAction()
+                return