Fix Google Calendar task sync reliability and rendering

[martin-forge]

Summary

This combines the Google Calendar fixes from #1802, #1832, #1843, and #1844 into one PR. I think they are easier to review together because they touch the same sync path and share metadata assumptions.

• Recurring task reschedules now keep one master event and one detached exception event, with EXDATEs for moved and completed instances.
• Zero-duration timed Google events get a minimal end time before FullCalendar list rendering, which prevents the multi-day display bug.
• Task deletions and failed sync writes are queued in plugin data and replayed after reconnect or restart; 404/410 deletes are treated as already clean.
• Create/update/status races are serialized or deduped so duplicate events and overwritten completion ticks are avoided.
• Calendar descriptions are plain text: wikilinks render as labels, and the Obsidian URL is included as text instead of an HTML anchor. This avoids raw HTML in Apple Calendar; whether it is clickable still depends on the calendar client.

Maintainer note

I opened this as a combined PR because these fixes all sit in the Google Calendar task sync path, and the later reliability fixes depend on the recurring-exception metadata from #1802. One merge should be simpler than sequencing four branches.

Validation

• npm test -- tests/services/TaskCalendarSyncService.test.ts tests/unit/issues/issue-google-calendar-delete-retry-queue.test.ts tests/unit/issues/issue-google-calendar-duplicate-investigation.test.ts tests/unit/issues/issue-google-calendar-archive-reliability.test.ts tests/unit/issues/issue-1696-gcal-recurring-reschedule.test.ts tests/unit/issues/issue-1696-local-calendar-recurring-reschedule.test.ts tests/unit/issues/issue-1823-zero-duration-google-calendar-list-duplication.test.ts --runInBand
• npm run typecheck
• npm run build:test
• TZ=UTC npm test -- --runInBand --silent

Note: a non-UTC local full test run still has two pre-existing timezone-sensitive failures in due-date-timezone-inconsistency.test.ts and issue-327-failing-test.test.ts; the UTC run passes.