[iCloud] Storage quota & CloudKit error handling

[zinkxx]

🎯 Goal

Gracefully handle CloudKit errors and iCloud storage limitations with clear user feedback.

📌 Scope

• Detect CloudKit errors (quota, network, permissions)
• Map errors to user-friendly messages
• Prevent infinite retry loops on fatal errors

🧠 Technical Notes

• Handle CKError types (quotaExceeded, networkUnavailable, permissionFailure)
• Conditional retry vs hard stop
• Centralized error handling layer

✅ Acceptance Criteria

• User is informed when iCloud storage is full
• Sync pauses when retrying is pointless
• App does not crash on CloudKit failures
• Clear recovery guidance is shown to the user