Filter cancelled calendar events before sync updates

[Ivanyanqi]

This PR addresses issue #315 (Invalid start time on calendar.events.update) by excluding cancelled Google events from the in-memory update set.

What changed

• After loading existing calendar events (showDeleted: false), filter out any events whose status is cancelled.
• Add a log line that reports how many cancelled events were filtered.

Why

Some recurring-event edge cases can still return cancelled events even with showDeleted=false. When those are treated as active and passed into update logic, they can trigger Invalid start time failures.

Scope

• Minimal runtime behavior change in startSync event-loading flow only.
• No config changes.

Validation

• Static logic validation against issue repro details and existing sync flow.
• Change is isolated to existing-event pre-processing before ID/MD5 mapping.

Closes #315

[Ivanyanqi]

This PR is a minimal fix for the recurring-event edge case behind Invalid start time.

It filters cancelled Google Calendar events before sync updates so they are never treated as active update targets.