Add native iOS app with offline privacy policy and available collections

[darrinm]

Summary

Adds an iPhone/iPad app that bundles the shared game for offline local play, with native sharing, invite entry, and online room transport. Version 1.0 build 4 also removes an empty ball collection and makes the privacy policy available offline.

• Add the UIKit/WebKit shell, loopback asset server, restricted native network bridge, and background/foreground handling.
• Prepare the audio graph and decode bundled samples in the background so first playback reuses prepared sounds.
• Hide Heads whenever the build has no head textures; saved Heads preferences fall back to Classic and keyboard cycling skips the unavailable collection.
• Bundle the published privacy page unchanged and open it from Settings in a dismissible local sheet that preserves the current game.
• Include the Xcode project, build/export instructions, privacy manifest, app icon, and App Store listing assets.

Validation

• All 361 JavaScript tests passed.
• All 3 native tests passed on iPhone 17 / iOS 26.5, covering bundled game/physics-worker startup, sound preparation, the collection picker, local privacy-page navigation, return to the existing game, lifecycle behavior, invite validation, and asset traversal rejection.
• Signed Release archive succeeded. Verified build number 4, the bundled privacy page and local Settings link, and the absence of private head textures.
• Version 1.0 build 4 uploaded successfully to App Store Connect; confirmed it appeared in TestFlight as Processing on September 19, 2026.
• Source tag: ios-v1.0-build4 (77bdddf).

Manual device touch/audio checks and longer play sessions remain listed in the iOS distribution guide. This PR does not submit the app for App Review.