Make the "Finish now?" button on session list work

src/web/tracker/models.py

@@ -1,5 +1,7 @@
 from django.db import models
-from datetime import timedelta
+from datetime import datetime
+from django.conf import settings
+from zoneinfo import ZoneInfo
 
 
 class Game(models.Model):
@@ -40,6 +42,9 @@ class Session(models.Model):
         mark = ", manual" if self.duration_manual != None else ""
         return f"{str(self.purchase)} {str(self.timestamp_start.date())} ({self.duration_any()}{mark})"
 
+    def finish_now(self):
+        self.timestamp_end = datetime.now(ZoneInfo(settings.TIME_ZONE))
+
     def duration_seconds(self):
         if self.timestamp_end == None or self.timestamp_start == None:
             if self.duration_manual == None: