feat(apple): add MacBook screenshot studio target

Add a Mac (16:10, 2880x1800) platform to the screenshot studio: a
MacBook .usdz model, native-app capture path in capture.sh (no simulator),
and all four marketing layouts. Fix the screen texturing so the capture
fills the display exactly — plain [0,1] planar UVs with a thin black matte
baked into the shot for the rounded-corner margin (replacing the UV
overscan that smeared the edge). Add a horizontal encryption-flow mode
(beams/stream) for the side-by-side laptops in stay-private.

packaging/apple/studio/assets/ATTRIBUTION.md

@@ -11,6 +11,11 @@
 - **Author:** lazercar (Sketchfab)
 - **License:** Creative Commons Attribution 4.0 (CC BY 4.0) — https://creativecommons.org/licenses/by/4.0/
 
+## macbook-air.usdz
+- **Title:** MacBook Air
+- **Author:** Jakob (Sketchfab — https://sketchfab.com/jakob3dlindblom)
+- **License:** Creative Commons Attribution 4.0 (CC BY 4.0) — https://creativecommons.org/licenses/by/4.0/
+
 CC BY 4.0 requires visible credit wherever these models (or renders derived from them)
 are published. The App Store screenshots produced by this studio are derivatives, so
 keep this attribution with the project. If a suitable place exists (e.g. the app's