fix: tray restart uses python -m for reliable process respawn

The previous os.execv approach and console_script detection both
failed on Windows. Now restart always spawns `python -m media_server.main`
via subprocess.Popen with start_new_session, which works regardless
of how the server was originally started.

media_server/tray.py

@@ -3,8 +3,6 @@
 import ctypes
 import io
 import logging
-import os
-import sys
 import webbrowser
 from pathlib import Path
 from typing import Callable
@@ -125,10 +123,13 @@ class TrayManager:
         if not _confirm("Media Server", "Restart the server?"):
             return
         logger.info("Restart requested from tray")
-        self._icon.stop()
+        self._restart_requested = True
         self._on_exit()
-        os.environ["MEDIA_SERVER_RESTART"] = "1"
-        os.execv(sys.executable, [sys.executable] + sys.argv)
+        self._icon.stop()
+
+    @property
+    def restart_requested(self) -> bool:
+        return getattr(self, "_restart_requested", False)
 
     def _shutdown(self, icon: "pystray.Icon", item: "pystray.MenuItem") -> None:
         if not _confirm("Media Server", "Shut down the server?"):