* fix(caldav): pull Google Calendar events from the events collection, not the /user principal
Google serves its CalDAV principal at .../caldav/v2/<id>/user but events live
under .../caldav/v2/<id>/events. The caldav library's principal->home-set
discovery does not reliably enumerate calendars from Google's /user endpoint,
so _sync_blocking fell into its 'treat the URL as a single calendar' fallback
and ran every calendar-query REPORT against the principal URL. /user holds no
VEVENTs, so the REPORT returned a clean but empty 200 for every date range:
auth succeeded, the calendar stayed empty (Apple Calendar works because iCloud
exposes standard discovery at the pasted URL).
Add _google_caldav_events_url() to map a recognised Google principal URL to its
events collection, and route both discovery-less fallbacks through
_open_url_as_calendar() so Google syncs hit /events while other servers' URLs
are used unchanged.
Fixes#2507
* fix(caldav): also map Google's legacy www.google.com/calendar/dav principal URL
Some Google accounts authenticate against the older CalDAV endpoint
(https://www.google.com/calendar/dav/<id>/user) rather than the newer
apidata.googleusercontent.com/caldav/v2 form (reported on #2507). Both have the
same principal-vs-events split, so map the legacy /user URL to its /events
collection as well. The legacy branch is gated on the /calendar/dav/ path so an
unrelated www.google.com URL ending in /user is left untouched.
L1