fix(ios): remove white frame from app icon by eliminating alpha channel

iOS renders transparent pixels as white, causing a white frame around the
app icon. This fix generates a 1024x1024 RGB PNG (no alpha channel) from
the existing build/icons/sq2160x2160.png source.

Changes:
- Add tools/generate-ios-icon.js script using Sharp to resize and remove alpha
- Add npm script 'generate:ios-icon' for reproducible icon generation
- Update AppIcon-512@2x.png to RGB format (was RGBA)
- Install Sharp as dev dependency for image processing

Icon is now fully opaque with correct brand blue color and white checkmark.

package.json

@@ -98,6 +98,7 @@
     "startFrontend:e2e": "npm run env && ng serve --port=4242",
     "startFrontend:prod": "npm run env && ng serve --configuration production",
     "startFrontend:stage": "npm run env && ng serve --configuration stage",
+    "generate:ios-icon": "node tools/generate-ios-icon.js",
     "sync:android": "npx cap sync android",
     "sync:ios": "npx cap sync ios",
     "dist:ios:prod": "npm run buildFrontend:prodWeb && npm run sync:ios",
@@ -256,6 +257,7 @@
     "pretty-quick": "^4.2.2",
     "query-string": "^7.1.3",
     "rxjs": "^7.8.2",
+    "sharp": "^0.34.5",
     "shepherd.js": "^11.2.0",
     "spark-md5": "^3.0.2",
     "stacktrace-js": "^2.0.2",