fix: A bug fix

Fixes #9485 /claim #9485

What this PR does

• Preserves UID between email and CalDAV events (prevents duplicate events)
• Adds SCHEDULE-AGENT=CLIENT to prevent Fastmail from sending duplicate invites
• Stops forcing UTC and preserves local timezone

Why

Fastmail was sending duplicate and UTC-only invitations because:

• Cal.com generated a new UID for CalDAV events
• Events were forced to UTC
• SCHEDULE-AGENT=CLIENT was missing