fix(ios): resolve getSharedImage() with null when no share pending

When no shared image exists, return a bare Capacitor resolve instead of
an object with null base64/fileName/shareId fields, matching the
TypeScript contract and web implementation.

ios/App/App/SharedImagePlugin.swift

@@ -34,17 +34,13 @@ public class SharedImagePlugin: CAPPlugin, CAPBridgedPlugin {
     
     /**
      * Get shared image data from App Group UserDefaults
-     * Returns base64 string, fileName, and shareId, or null fields if no image exists
+     * Returns base64 string, fileName, and shareId, or null if no image exists
      * Read-only: native metadata and file are left intact after retrieval (Phase 1C)
      */
     @objc public func getSharedImage(_ call: CAPPluginCall) {
         guard let sharedData = SharedImageUtility.getSharedImageData() else {
             // No shared image exists - return null (not an error)
-            call.resolve([
-                "base64": NSNull(),
-                "fileName": NSNull(),
-                "shareId": NSNull()
-            ])
+            call.resolve()
             return
         }