replace react-nav header hack with scroll edge interaction module

- new expo-scroll-edge-interaction native module (iOS-only) that sets up
  UIScrollEdgeElementContainerInteraction on iOS 26+
- new ScrollEdgeInteractionProvider context and hooks
- Layout.Screen gains `transparentHeader` prop
- Layout.Header.Outer auto-detects transparent mode from context
- List auto-registers scroll view and applies content inset

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

modules/expo-scroll-edge-interaction/ios/ExpoScrollEdgeInteraction.podspec

@@ -0,0 +1,21 @@
+Pod::Spec.new do |s|
+  s.name           = 'ExpoScrollEdgeInteraction'
+  s.version        = '1.0.0'
+  s.summary        = 'UIScrollEdgeElementContainerInteraction for React Native views'
+  s.description    = 'UIScrollEdgeElementContainerInteraction for React Native views'
+  s.author         = 'bluesky-social'
+  s.homepage       = 'https://github.com/bluesky-social/social-app'
+  s.platforms      = { :ios => '13.4', :tvos => '13.4' }
+  s.source         = { git: '' }
+  s.static_framework = true
+
+  s.dependency 'ExpoModulesCore'
+
+  # Swift/Objective-C compatibility
+  s.pod_target_xcconfig = {
+    'DEFINES_MODULE' => 'YES',
+    'SWIFT_COMPILATION_MODE' => 'wholemodule'
+  }
+
+  s.source_files = "**/*.{h,m,mm,swift,hpp,cpp}"
+end