feat: add connection groups and tags to iOS app

[datlechin]

Summary

• Add connection groups and tags support to TablePro Mobile (iOS)
• Enrich shared TableProCore models: ConnectionColor enum, ConnectionGroup with color/parentId, ConnectionTag with color/isPreset/presets, DatabaseConnection with tagId
• Extend SyncRecordMapper and IOSSyncCoordinator to sync groups and tags via CloudKit alongside connections
• New iOS views: segmented Groups/All list, tag filter chips, tag pills on connection rows, group/tag pickers in connection form, group and tag management screens

Changes

• 7 new files: ConnectionColor, GroupPersistence, TagPersistence, ConnectionColorPicker, GroupFormSheet, TagFormSheet, GroupManagementView, TagManagementView
• 11 modified files: ConnectionGroup, ConnectionTag, DatabaseConnection, SyncRecordType, SyncRecordMapper, AppState, IOSSyncCoordinator, ConnectionListView, ConnectionFormView, OnboardingView, TableProMobileApp
• No macOS changes — macOS app has its own local model types

Test plan

• Build iOS app on simulator
• Create groups and tags on iOS — verify persistence across app restart
• Assign group/tag to connection via form — verify display in list
• Test segmented Groups/All view modes
• Test tag filter chips (tap to filter, tap again to deselect)
• Test group/tag management (create, edit, reorder, delete)
• Test delete cascade (deleting group nullifies groupId on connections)
• Test preset tag protection (cannot delete)
• Test iCloud sync: create groups/tags on macOS → verify they appear on iOS
• Test iCloud sync: create groups/tags on iOS → verify they appear on macOS