The "Nächste Veranstaltungen" table read the event URL via `ICAL.Event.url`,
but ical.js does not expose a `url` getter on `ICAL.Event` (it only has uid,
summary, description, color, location, sequence, the dates, organizer and
attendees). `event.url` was therefore always `undefined` and the `?? ""`
fallback turned it into an empty string, so every row rendered as
`<a href="">`, a dead link that just reloads the start page.
Read the URL from the VEVENT component instead. This also picks up the
`URL;VALUE=URI:` form used by most events in the published calendar, which is
exported from a CalDAV client and does not use a bare `URL:` property.
Not every event has a URL, so only wrap the name in a link when one is
present and emit plain text otherwise.
Checked against https://berlin.ccc.de/calendars/all.ics (31 events, 1 of them
without a URL):
before: <td><a href="">CCCB Plenum</a></td>
after: <td><a href="https://wiki.berlin.ccc.de/Plenum">CCCB Plenum</a></td>
after: <td>Aktionstag gegen Überwachung im Chaos Computer Club Berlin</td>
Fixes: c28f04c6e8 ("switch to ics files; make calendars work; fix some minor issues")
Assisted-by: Claude:claude-opus-5
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
