fix(calendar): classify self-organized imported events as editable via organizerCalendarAddress fallback

[krisatverbidio]

Summary

isOrganizer previously only recognized the current user as an event organizer when a participant carried the roles.owner flag. Self-organized events imported from other servers (e.g. Zimbra) using Vandelay don't set that flag - they convey the organizer at the event level via organizerCalendarAddress (or replyTo) instead. This PR adds a fallback so those events are correctly identified as organized by the user.

Changes

• Added a getEventOrganizerEmails helper that collects event-level organizer addresses from organizerCalendarAddress and replyTo, stripping the mailto: prefix and normalizing to lowercase.
• Reworked isOrganizer to check participant roles.owner first, then fall back to matching the event-level organizer address(es) against the user's emails.
• Changed the early-return guard from !event.participants to userEmails.length === 0, so events with no participants can still match via the organizer-address fallback.
• Added tests covering the organizerCalendarAddress match (including case-insensitivity), the replyTo fallback, and the negative case where the organizer is someone else.

Related Issues

Fixes #525

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor / code quality improvement
• Chore / dependency update / CI change

Checklist

• I have read the Contributing Guide
• My code follows the project's code style and conventions
• I have run npm run typecheck && npm run lint and there are no errors
• The build passes (npm run build)
• I have tested my changes locally
• I have added or updated documentation if needed
• I have updated translations (locales/) if my changes affect user-facing text
• I have included screenshots or a screen recording for UI changes