feat(ios): add iCloud sync toggle, default page size, and default safe mode to Settings

[datlechin]

Summary

Settings was sparse: just analytics + Face ID. This PR adds the three most-requested config knobs and threads them through the consumers.

iCloud Sync toggle

• New @AppStorage("com.TablePro.settings.cloudSyncEnabled") (default true)
• Sync entry points gated:
  • TableProMobileApp.scenePhase .active → skip the auto-sync Task when off
  • ConnectionListView toolbar Sync button → disables and swaps arrow.triangle.2.circlepath.icloud for icloud.slash when off
  • ConnectionListView pull-to-refresh → no-op when off
• Onboarding's "Sync from iCloud" button is intentionally not gated (defaults are still in effect when onboarding runs, and the button is an explicit user-initiated import)
• Existing iCloud data is not deleted; the toggle just stops further pushes/pulls

Rows per Page (default page size)

• New @AppStorage("com.TablePro.settings.defaultPageSize") (default 100)
• Picker with 50 / 100 / 200 / 500 options
• DataBrowserViewModel.init reads the setting on construction. The toolbar's "Rows per Page" submenu still lets users override per session

Default Safe Mode

• New @AppStorage("com.TablePro.settings.defaultSafeMode") (default .off)
• Picker iterates SafeModeLevel.allCases
• ConnectionFormViewModel.init(editing:) applies the default when editing == nil (new connection); when editing existing, the connection's stored level wins

Plumbing

• New Platform/AppPreferences.swift enum centralizes the keys, defaults, and pageSizeOptions: [Int]. Both the View (via @AppStorage(AppPreferences.xxxKey)) and the consumers (via AppPreferences.isCloudSyncEnabled / defaultPageSize / defaultSafeMode) read the same constants

Test plan

• Settings: iCloud Sync off → ConnectionList sync button greys out and shows icloud.slash. Pull to refresh does nothing. Cold launch with sync off does not call syncCoordinator.sync. Toggle on → sync resumes immediately
• Settings: change Rows per Page to 200 → open a new table → bottom-bar shows "1-200 of N", pagination respects 200
• Settings: change Default Safe Mode to Read Only → tap "+" to add new connection → safe mode picker is pre-selected to Read Only. Edit an existing connection: its stored level is preserved