feat: iCloud sync for connections, tags, settings, and templates

[datlechin]

Summary

• Add opt-in iCloud sync (Settings > General) using NSUbiquitousKeyValueStore with a protocol-based SyncEngine architecture
• Sync connections (metadata only), tags, all 5 settings domains, and table templates across Macs — passwords stay in local Keychain
• Three-way conflict detection with a SwiftUI conflict resolution sheet (keep local / keep remote)
• Password badge indicator on synced connections that need local password entry
• triggeredBySync parameter on storage save methods to prevent sync feedback loops

New Files

File	Purpose
Core/Sync/SyncEngine.swift	Protocol + SyncEnvelope + SyncDataType + SyncError
Core/Sync/ICloudSyncEngine.swift	NSUbiquitousKeyValueStore implementation
Core/Sync/SyncCoordinator.swift	Central coordinator (storage ↔ iCloud)
Core/Sync/SyncConflict.swift	Conflict model + ConflictResolution enum
Views/Sync/SyncConflictResolutionView.swift	Conflict resolution UI
TablePro.entitlements	iCloud KV store entitlement

Modified Files

• AppSettings.swift — added iCloudSyncEnabled to GeneralSettings
• ConnectionStorage.swift / TagStorage.swift / TableTemplateStorage.swift — sync hooks with triggeredBySync guard
• AppSettingsManager.swift — sync hooks on all 5 settings domains
• GeneralSettingsView.swift — iCloud Sync UI section
• WelcomeWindowView.swift — password key badge for synced connections
• OpenTableApp.swift — SyncCoordinator startup
• project.pbxproj — entitlements linked for Debug + Release

Test plan

• Enable iCloud sync toggle in Settings > General
• Verify connections, tags, settings, and templates sync to a second Mac
• Modify data on both Macs simultaneously to trigger conflict resolution
• Verify passwords are NOT synced — synced connections show key badge
• Disable sync and verify no further pushes occur
• Test with iCloud signed out — toggle should be disabled with warning