Use Conference.hostname in .ics export instead of hardcoded host

The favourites-calendar .ics export hardcoded https://2026.pycon.it for
the event description Info line and the URL property. Build the URL from
the per-conference hostname field (added in #4662) so the link is correct
for any conference.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: marcoacierno

backend/schedule/tests/test_views.py

@@ -20,7 +20,9 @@
 
 def test_user_schedule_item_favourites_calendar(client):
     user = UserFactory()
-    conference = ConferenceFactory(timezone=zoneinfo.ZoneInfo("Europe/Rome"))
+    conference = ConferenceFactory(
+        hostname="2026.pycon.it", timezone=zoneinfo.ZoneInfo("Europe/Rome")
+    )
     second_conf = ConferenceFactory()
 
     schedule_item_1 = ScheduleItemFactory(
@@ -159,7 +161,7 @@ def test_user_schedule_item_favourites_calendar(client):
 Language/Lingua: English
 Speaker(s)/Relatore(i): Jane Doe, John
 Room(s)/Stanza(e): Room Name
-Info: https://2026.pycon.it/event/{schedule_item_1.slug}/
+Info: https://{conference.hostname}/event/{schedule_item_1.slug}/
 """.strip()
     )
     assert event_schedule_item_1.get("dtstart").dt == datetime(
@@ -182,7 +184,7 @@ def test_user_schedule_item_favourites_calendar(client):
 Session format/Formato: Panel
 Language/Lingua: Italian
 Room(s)/Stanza(e): Another Room
-Info: https://2026.pycon.it/event/{schedule_no_speaker.slug}/
+Info: https://{conference.hostname}/event/{schedule_no_speaker.slug}/
 """.strip()
     )
 

backend/schedule/views.py

@@ -60,9 +60,9 @@ def user_schedule_item_favourites_calendar(request, conference_id, hash_user_id)
 
         event_description += f"\nRoom(s)/Stanza(e): {rooms}"
 
-        event_description += (
-            f"\nInfo: https://2026.pycon.it/event/{schedule_item.slug}/"
-        )
+        event_url = f"https://{conference.hostname}/event/{schedule_item.slug}/"
+
+        event_description += f"\nInfo: {event_url}"
 
         event = Event()
         event.add("summary", f"[{conference_name}] {schedule_item.title}")
@@ -77,7 +77,7 @@ def user_schedule_item_favourites_calendar(request, conference_id, hash_user_id)
                 " ", ""
             ),
         )
-        event.add("url", f"https://2026.pycon.it/event/{schedule_item.slug}/")
+        event.add("url", event_url)
         event.add(
             "dtstart",
             schedule_item.start.replace(tzinfo=conference_timezone).astimezone(utc),