chore(apple): add screenshot studio

packaging/apple/studio/README.md

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+# App Store screenshot studio
+
+Code-driven, fully local App Store screenshots. **Typst** composes each frame
+(gradient background + blank device mockup + app screenshot + localized caption)
+and renders it to an exact-size PNG. Captions come from `strings.json` (9 locales);
+app screenshots come from the real app (see capture, step 3).
+
+## Requirements
+- `typst` (0.15+) — installed.
+- `imagemagick` — only for the tilted hero shot's perspective warp (step 2). `brew install imagemagick`.
+
+## Render
+```sh
+./build.sh                                  # all locales × screens -> generated/<Language>/
+./build.sh --publish                        # -> ../<Language>/ (ships to App Store)
+LOCALES="fr de" SCREENS="share-securely" ./build.sh
+```
+Default writes to `generated/` (safe). `--publish` overwrites the real language folders.
+
+Single frame while tuning:
+```sh
+typst compile screens.typ out.png --input locale=fr --input screen=share-securely --ppi 72
+```
+
+## Files
+- `strings.json` — captions per locale (first-pass translations; review before shipping).
+- `screens.typ` — the composition + per-screen layout data (`screens` dict). Tweak numbers, re-run.
+- `build.sh` — loops locales × screens; maps locale→folder and screen→filename.
+- `assets/mockup-straight.png` — blank straight device (real alpha, black screen).
+- `assets/mockup-rotated.png` — blank tilted device (for the hero shot).
+- `assets/globe.png` — circle-clipped in Typst (the export has a baked checkerboard, not true alpha).
+- `assets/shots/<locale>/<screen>.png` — captured app screenshots (optional; placeholder if absent).
+
+## How the screenshot gets into the phone
+The mockup's screen glass is a rectangle. `screens.typ` places the screenshot inset
+into that rectangle (`sx`/`sy`/`sr` fractions) with the bezel framing it. Measure those
+fractions once against `mockup-straight.png`.
+
+## Full pipeline
+```sh
+./capture.sh     # real localized app screens -> assets/shots/<locale>/<screen>.png
+./build.sh       # composite everything -> generated/<Language>/
+./build.sh --publish   # when happy -> ships to ../<Language>/
+```
+`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. Screen ⇄ scenario map:
+`share-securely`→`share`, `choose-receivers`→`approval`, `send-anywhere`→`transfer-details`.
+
+## Status
+1. ✅ Typst + JSON + straight-mockup compositing.
+2. ✅ Tilted hero (`send-anywhere`): `warp.sh` perspective-warps the screenshot onto the
+   rotated mockup's screen quad (4 auto-detected corners); `build.sh` runs it automatically.
+3. ✅ Transparent globe layer (placed directly — use the alpha export, not a flattened one).
+4. ✅ Screenshot capture: `capture.sh` + the `#if DEBUG` fixture gateway, per locale, deterministic.
+5. ⬜ Ribbon art layer for `stay-private` (export as its own transparent PNG).
+6. ⬜ Layout polish: tune device positions/sizes in `screens.typ` against the originals.