docs(apple): document Mac target in screenshot studio README

packaging/apple/studio/README.md

@@ -15,7 +15,10 @@ swift run studio                      # all locales × screens -> generated/<Lan
 swift run studio --publish            # -> ../<Language>/ (ships to App Store)
 LOCALES="fr de" SCREENS="share-securely" swift run studio        # subset
 PLATFORM=ipad swift run studio        # iPad set -> generated/<Language>/iPad/
+PLATFORM=mac swift run studio         # Mac set  -> generated/<Language>/Mac/
 ```
+`PLATFORM` must match between `capture.sh` and `swift run studio` (they read the same
+`generated/shots/<platform>/` tree).
 Run from this directory (it reads `strings.json` and `assets/` relative to cwd).
 
 ## Full pipeline
@@ -26,37 +29,48 @@ swift run studio    # composite everything -> generated/<Language>/[iPad/]
 ```
 `capture.sh` drives the app into each screen via the DEBUG `-VniScreenshot` launch
 argument (see `apple/VniDrop/App/ScreenshotSupport.swift`), once per locale via
-`-AppleLanguages`, in dark mode with a 9:41 status bar. Screenshots are transient
+`-AppleLanguages`, in dark mode. Screenshots are transient (git-ignored, regenerated per
-(git-ignored, regenerated per run) — during layout iteration, capture once then re-run
+run) — during layout iteration, capture once then re-run `swift run studio` on its own.
-`swift run studio` on its own.
+- **iPhone / iPad** run in the simulator (9:41 status-bar override) via `simctl`.
+- **Mac** has no simulator: `capture.sh` builds the native app, launches the binary
+  directly, sizes its window with `osascript`, and grabs it with `screencapture`. Grant
+  the terminal **Accessibility + Screen Recording** permission the first time.
 
 ## Platforms
-`PLATFORM=iphone` (default) or `ipad`. Each `Platform` (`Sources/studio/Platform.swift`)
+`PLATFORM=iphone` (default), `ipad`, or `mac`. Each `Platform`
-carries its canvas size, capture simulator, output subfolder, and a `DeviceModel` — the
+(`Sources/studio/Platform.swift`) carries its canvas size, capture target, output
-`.usdz`, its screen material, the orientation fix (yaw so the screen faces the camera),
+subfolder, and a `DeviceModel` — the `.usdz`, its screen material, the orientation fix
-optional front-glass mesh to hide, and whether to tint the body graphite. Adding a device
+(yaw so the screen faces the camera), optional front-glass mesh to hide, whether to tint
-(e.g. Mac) is a new `DeviceModel` + `Platform` case + a layout set.
+the body graphite, a `fillFraction` (how much of the frame the device fills; lower for
+wide 3/4 poses that would otherwise clip), and a `screenPad` (black margin baked around
+the shot so the window clears the display's rounded corners). Adding a device is a new
+`DeviceModel` + `Platform` case + a layout set. (The studio is Apple-only today; the
+same SwiftUI/SceneKit approach is intended to extend to Android and Windows later.)
 
 ## Device rendering
 `SceneKitDeviceRenderer` textures the captured screenshot onto the model's screen mesh and
 renders it off-screen. Curvature, bezel and body are the model's real geometry; poses
 (pitch/yaw/roll) and a studio environment (IBL + bloom) are applied in the scene. It
-auto-generates planar UVs for screen meshes that ship without them.
+auto-generates planar `[0,1]` UVs for screen meshes that ship without them, and mattes the
+shot onto a slightly larger black canvas (`screenPad`) so the display edge stays black
+instead of smearing the capture's corner pixels.
 
 ## Assets (`assets/`)
-- `iphone-17-pro-max.usdz`, `ipad-pro.usdz` — the 3D devices (committed; CC BY 4.0, see
+- `iphone-17-pro-max.usdz`, `ipad-pro.usdz`, `macbook-air.usdz` — the 3D devices
-  `ATTRIBUTION.md`).
+  (committed; CC BY 4.0, see `ATTRIBUTION.md`).
 - `globe.png` — for the send-anywhere hero (committed).
 - `generated/shots/<platform>/<locale>/*.png` — captured app screens (transient).
 
 ## Layout & tuning
-- `Sources/studio/ScreenSpec.swift` — per-platform layouts (`iphone` / `ipad`): gradient,
+- `Sources/studio/ScreenSpec.swift` — per-platform layouts (`iphone` / `ipad` / `mac`):
-  device pose/position/size, globe + route (send-anywhere), the encryption flow
+  gradient, device pose/position/size, globe + route (send-anywhere), the encryption flow
-  (stay-private: `beams` → `lock` → `stream` + `banners`), caption placement.
+  (stay-private: `beams` → `lock` → `stream` + `banners`), caption placement. `beams` and
+  `stream` take a `horizontal` flag for side-by-side devices (used by Mac stay-private).
 - `Sources/studio/ScreenFrame.swift` — the composition (layer order, caption fitting,
   generated artwork).
 
 ## Screens
 `share-securely`, `choose-receivers`, `send-anywhere` (globe + Paris→LA route arc,
-reuses the share screenshot), `stay-private` (two stacked phones + encryption beams →
+reuses the share screenshot), `stay-private` (encryption beams → padlock → binary
-padlock → binary protection stream, with localized CHIFFREMENT/PROTECTION banners).
+protection stream, with localized CHIFFREMENT/PROTECTION banners; two stacked phones on
+iPhone/iPad, two side-by-side laptops with a horizontal flow on Mac).