feat: backfill historical university calendar events from 25Live

[jaspermayone]

Problem

The UniversityCalendarIcsService syncs events from the 25Live ICS feed (https://25livepub.collegenet.com/calendars/wit-main-events-calendar.ics), but 25Live only publishes upcoming events. This means any historical events (past holidays, term dates, etc.) were never imported and are absent from the database.

Goal

As part of the 25Live integration project, we should backfill historical university calendar events so the database has a complete record.

Possible Approaches

• 25Live Publisher API — 25Live has a publisher API that may support date range queries. Investigate whether we can request events older than today by passing a date range parameter to the feed URL (e.g., startdate / enddate query params).
• Archived ICS snapshots — If anyone has a cached .ics from a previous scrape, it can be piped through UniversityCalendarIcsService directly.
• Rake task / one-off import — Write a task that accepts an ICS URL or file path and imports it, so we can re-run backfills as needed.

Acceptance Criteria

• Investigate whether the 25Live feed supports historical date range queries
• If supported, implement a way to fetch and import events for a given date range
• Add a rake task or admin action to trigger a historical backfill
• Ensure the existing duplicate-detection logic in UniversityCalendarIcsService handles re-importing without creating duplicates

[jaspermayone]

We're going to do this through the 25live service we're writing.