feat(studio): native SwiftUI + SceneKit App Store screenshot pipeline

Replace the Typst/ImageMagick studio with a SwiftPM executable that composes
each marketing screen as a SwiftUI view and renders it headlessly via
ImageRenderer to exact 1284x2778 PNGs.

- Devices are a real iPhone 17 Pro Max .usdz textured + posed in SceneKit
  (graphite body, studio IBL); screen curvature/bezel are the model's geometry.
- Per-screen layouts (pose, globe, route arc, encryption flow) in ScreenSpec.
- send-anywhere: globe + Paris->LA route arc; uses the app's share screen.
- stay-private: converging beams -> glowing padlock -> binary protection stream,
  with localized CHIFFREMENT/PROTECTION banners and an auto-sizing header panel.
- Captions auto-shrink per locale (ViewThatFits) so long translations never clip.
- Screenshots are transient (generated/shots, git-ignored), captured per locale;
  generate.sh does capture + composite in one shot.
- Commit the .usdz model (CC BY 4.0, see assets/ATTRIBUTION.md) and globe asset.
- Remove the superseded Typst pipeline (screens.typ, build.sh, frame.sh, warp.sh).

packaging/apple/studio/.gitignore

@@ -1,8 +1,8 @@
 generated/
 out-*.png
-assets/shots/**/*.png
+.build/
+.swiftpm/
+# Only the DEVICE=2d fallback mockups are ignored; the globe + 3D model are committed
+# because the default pipeline needs them.
 assets/mockup-*.png
 assets/mask-*.png
-assets/globe.png
-assets/ribbon.png
-!assets/README.md