gallery: link PhotosUI in podspec so the limited-picker category loads

Swift `import PhotosUI` made the compiler happy but the binary never
referenced any PhotosUI symbol directly — `presentLimitedLibraryPicker`
is dispatched via `objc_msgSend` against an Obj-C category on
`PHPhotoLibrary`. Without an explicit framework link the linker
dropped PhotosUI, the category never registered, and iOS 26 raised
NSInvalidArgumentException for an "unrecognized selector".

Declare Photos + PhotosUI as podspec frameworks so the linker force-
loads them.

ios/ux.podspec

@@ -7,6 +7,7 @@ Pod::Spec.new do |s|
   s.author           = { 'Swipelab' => 'hello@swipelab.co' }
   s.source           = { :path => '.' }
   s.source_files     = 'Classes/**/*.swift'
+  s.frameworks       = ['Photos', 'PhotosUI']
   s.dependency 'Flutter'
   s.ios.deployment_target = '13.0'
   s.swift_version = '5.0'