Implement CloudKit Sync Service

[DrunkOnJava]

📋 Sub-task of #97

Description

Replace mock CloudService with real CloudKit implementation for data synchronization across devices.

Current State

• CloudService.swift uses mock implementation
• No actual cloud sync functionality
• Falls back to local storage only

Implementation Tasks

• Configure CloudKit container and schema
• Implement CloudKitService conforming to CloudService protocol
• Add record types for all entities (Item, Location, Photo, Receipt)
• Implement sync engine with conflict resolution
• Add offline queue for pending changes
• Implement subscription for real-time updates
• Add progress tracking for sync operations

CloudKit Schema Design

Record Types:
- Item (fields: name, category, value, etc.)
- Location (fields: name, parentReference)
- Photo (fields: itemReference, imageAsset)
- Receipt (fields: store, date, amount, items)

Key Features

• Automatic sync on app launch
• Background sync when data changes
• Conflict resolution (last-write-wins)
• Batch operations for efficiency
• Progress indicators for users
• Error recovery mechanisms

Technical Requirements

• Enable CloudKit capability in project
• Create CKContainer configuration
• Implement CKRecord extensions for models
• Add sync status to UI
• Handle account changes
• Implement data migration

Testing Requirements

• Test sync between multiple devices
• Test conflict resolution
• Test offline/online transitions
• Test large dataset sync
• Test account switching

Performance Goals

• Sync 1000 items < 30 seconds
• Incremental sync < 5 seconds
• Offline queue handling

Estimated Effort: 1 week

[DrunkOnJava]

Closing: This issue has been resolved/superseded by the complete modular architecture restructure now in main branch (commit 33a0ead). The new architecture implements a comprehensive solution that addresses the core needs this issue was tracking.