Add iOS peek long-press context menu for image embeds

Introduces expo-bluesky-context-menu, a compositional Root/Trigger/Menu/MenuItem
wrapper around UIContextMenuInteraction. The preview ViewController is sized to
the image's true aspect ratio so tall/panorama previews don't stretch mid-lift,
and menu icons are rasterized from the app's SVG icon set on the native side.

The preview prop is a discriminated union (image today; video and externalCard
reserved) so the same module can back those embeds in follow-ups.

https://claude.ai/code/session_015REmux3R9uuEMMJUHxTyQT

modules/expo-bluesky-context-menu/ios/ExpoBlueskyContextMenu.podspec

@@ -0,0 +1,20 @@
+Pod::Spec.new do |s|
+  s.name           = 'ExpoBlueskyContextMenu'
+  s.version        = '1.0.0'
+  s.summary        = 'Native iOS context menu (peek + long-press) for embeds'
+  s.description    = 'Wraps UIContextMenuInteraction with a compositional JS API.'
+  s.author         = ''
+  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'
+
+  s.pod_target_xcconfig = {
+    'DEFINES_MODULE' => 'YES',
+    'SWIFT_COMPILATION_MODE' => 'wholemodule'
+  }
+
+  s.source_files = "**/*.{h,m,mm,swift,hpp,cpp}"
+end