add iOS communication notifications for chat with sender avatars

Uses INSendMessageIntent to display sender profile pictures in DM
notifications. The NSE downloads the avatar thumbnail and creates a
Communication Notification, falling back gracefully if the download
fails or the avatar URL is absent.

Also adds chat-reaction support to the notification handler on both
iOS and Android.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/BlueskyNSE/Info.plist

@@ -8,6 +8,13 @@
       <string>com.apple.usernotifications.service</string>
       <key>NSExtensionPrincipalClass</key>
       <string>$(PRODUCT_MODULE_NAME).NotificationService</string>
+      <key>NSExtensionAttributes</key>
+      <dict>
+        <key>IntentsSupported</key>
+        <array>
+          <string>INSendMessageIntent</string>
+        </array>
+      </dict>
     </dict>
     <key>MainAppScheme</key>
     <string>bluesky</string>