feat(pos-pwa): pOS: make TPV installable PWA and launch fullscreen

work/artifacts/POS-PWA/implementer.md

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+# Implementer — POS-PWA
+
+## Summary
+Added PWA manifest and viewport/theme_color to POS app.
+
+## Files
+- `app/manifest.ts`: PWA manifest with standalone display, theme_color #70AD47
+- `app/layout.tsx`: added viewport export with themeColor, appleWebApp config, manifest link
+
+## Note
+Removed `themeColor` from metadata export (unsupported by Next.js 16) — it now lives only in the `viewport` export.
+
+## Validation
+- `cd project/apps/pos && npm run build` ✅ (no warnings)
+- `/manifest.webmanifest` generated as static page
+- `git diff --check` ✅