PR #539 fixed date-range filtering so events outside the queried range
are excluded. However, recurring events still returned the master event
with its original DTSTART instead of expanded occurrences.
Add <C:expand> element to CalDAV REPORT requests (RFC 4791 §9.6.5) when
both date bounds are provided, so the server returns one VEVENT per
occurrence with the correct DTSTART. Refactor VEVENT parsing into a
shared helper and add _parse_all_ical_events() to handle multi-VEVENT
responses from expanded results.
Closes#538
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>