fix: query holidays by term date range instead of term_id

Holidays that fall between semesters (winter break, spring break, etc.)
have no term_id because they fall outside any term's start_date..end_date
window. Filtering by term_id excluded them entirely. Now we query all
holidays within the date range spanned by the user's enrolled terms.

Author: jaspermayone

app/controllers/calendars_controller.rb

@@ -182,8 +182,13 @@ def add_university_events(cal)
     enrolled_term_ids = @courses.map(&:term_id).compact.uniq
     return if enrolled_term_ids.empty?
 
-    UniversityCalendarEvent.holidays.where(term_id: enrolled_term_ids).find_each do |event|
-      add_university_event_to_calendar(cal, event, force_all_day: true)
+    terms = Term.where(id: enrolled_term_ids).where.not(start_date: nil).where.not(end_date: nil)
+    if terms.any?
+      min_date = terms.minimum(:start_date)
+      max_date = terms.maximum(:end_date)
+      UniversityCalendarEvent.holidays.in_date_range(min_date, max_date).find_each do |event|
+        add_university_event_to_calendar(cal, event, force_all_day: true)
+      end
     end
 
     user_config = @user.user_extension_config