fix(share): attach captured card image when sharing to Instagram Stories

Both share modals opened the instagram-stories:// scheme without ever
placing the captured PNG on the pasteboard, so Instagram opened an empty
story. Replace the manual scheme launch with react-native-share
shareSingle(INSTAGRAM_STORIES), which writes the image to UIPasteboard
under com.instagram.sharedSticker.backgroundImage on iOS and uses the
ADD_TO_STORY intent on Android. Gate the flow on the required Facebook
App ID (EXPO_PUBLIC_FACEBOOK_APP_ID) and Instagram being installed, with
fallback to the system share sheet, and remove the dead base64 reads.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/mobile/android/app/src/main/AndroidManifest.xml

@@ -15,6 +15,7 @@
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
   <uses-permission android:name="com.android.vending.BILLING"/>
   <queries>
+    <package android:name="com.instagram.android"/>
     <intent>
       <action android:name="android.intent.action.VIEW"/>
       <category android:name="android.intent.category.BROWSABLE"/>