Replace pytz with zoneinfo for timezone handling

Fixes ModuleNotFoundError by using Python's built-in zoneinfo module
instead of the external pytz dependency. zoneinfo is the standard
library solution for timezone handling in Python 3.9+.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tasks/views.py

@@ -219,12 +219,12 @@ class DashboardView(View):
             return redirect('login')
 
         # Get today's date in user's timezone
-        import pytz
+        from zoneinfo import ZoneInfo
         try:
-            user_tz = pytz.timezone(request.user.timezone)
+            user_tz = ZoneInfo(request.user.timezone)
             user_now = timezone.now().astimezone(user_tz)
             today = user_now.date()
-        except (pytz.UnknownTimeZoneError, AttributeError):
+        except (Exception,):
             # Fall back to UTC if user timezone is invalid or missing
             today = timezone.now().date()