Fix overdue detection ignoring due_time, harden SW precache installs

Task.is_overdue only compared due_date to today, so a task due at 9am
stayed "not overdue" until midnight regardless of due_time (Gitea #7).
Now factors in due_time when the due date is today, mirrored in the
offline app's isTaskOverdue().

Also hardened the service worker's install step: cache.addAll() lets
the browser's HTTP cache satisfy each precache fetch, and since static
assets here send no Cache-Control/ETag (just Last-Modified), a
CACHE_NAME bump wasn't reliably guaranteed to pick up fresh files.
Forcing {cache: 'reload'} on each precache fetch fixes that.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tasks/models.py

@@ -155,16 +155,19 @@ class Task(models.Model):
             from django.utils import timezone
             from zoneinfo import ZoneInfo
 
-            # Get current date in user's timezone
+            # Get current date/time in user's timezone
             try:
                 user_tz = ZoneInfo(self.user.timezone)
                 user_now = timezone.now().astimezone(user_tz)
-                user_today = user_now.date()
             except (Exception,):
                 # Fall back to UTC if user timezone is invalid or missing
-                user_today = timezone.now().date()
+                user_now = timezone.now()
 
-            return self.due_date < user_today
+            if self.due_date < user_now.date():
+                return True
+            if self.due_date == user_now.date() and self.due_time:
+                return self.due_time < user_now.time()
+            return False
         return False
 
     @property