Fix Google Calendar event rendering edge cases

[martin-forge]

Summary

• Fix zero-duration Google Calendar events rendering across multiple days in list views. Closes [Bug]: Google Calendar zero-duration recurring exception can render on two days in list view #1823.
• Preserve original provider event data for context menus/debugging.
• Export task descriptions as plain text with wikilink labels and a visible Obsidian URI.

Validation

• npm run lint
• npm test -- tests/services/TaskCalendarSyncService.test.ts tests/unit/issues/issue-1823-zero-duration-google-calendar-list-duplication.test.ts --runInBand
• npm run typecheck
• npm run build

[callumalpass]

Thank you @martin-forge ! Much appreciated--merging for the next release.