Add start/end time fields to CalendarEvent (#28) (#29)

## Summary
Closes #28.

- Add optional `start_time` / `end_time` (`TimeField`) on `CalendarEvent`
- Expose times in Django admin list + form
- Replace hardcoded calendar template times with `time_range_display`
- Add migration `0013` and unit coverage for time formatting

## Test plan
- [ ] `python manage.py migrate`
- [ ] `python manage.py test schasite.tests.CalendarEventTests`
- [ ] In admin, edit an event with start/end times and confirm calendar page shows them
- [ ] Confirm events without times hide the Time rowReviewed-on: #29

schasite/models.py

@@ -66,6 +66,8 @@ class CalendarEvent(TimeInfoBase):
     event_name = models.CharField(max_length=256)
     start_date = models.DateField(blank=True, null=True)
     end_date = models.DateField(blank=True, null=True)
+    start_time = models.TimeField(blank=True, null=True)
+    end_time = models.TimeField(blank=True, null=True)
     location_name = models.CharField(max_length=256, blank=True, null=True)
     coordinator_email = models.EmailField(max_length=256, blank=True, null=True)
     event_link_name = models.CharField(max_length=64, blank=True, null=True)
@@ -90,6 +92,19 @@ class CalendarEvent(TimeInfoBase):
     def no_date(self):
         return not self.has_date()
 
+    def time_range_display(self):
+        """Format start/end times for templates, e.g. '11:00 AM - 3:00 PM'."""
+        from django.utils.formats import time_format
+
+        if not self.start_time and not self.end_time:
+            return ""
+
+        start = time_format(self.start_time, "g:i A") if self.start_time else ""
+        end = time_format(self.end_time, "g:i A") if self.end_time else ""
+        if start and end:
+            return f"{start} - {end}"
+        return start or end
+
 
 class CalendarEventAddressModel(TimeInfoBase):
     calendar_event = models.OneToOneField(CalendarEvent, on_delete=models.CASCADE)