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/ExpoBlueskyContextMenuModule.swift

@@ -0,0 +1,23 @@
+import ExpoModulesCore
+
+public class ExpoBlueskyContextMenuModule: Module {
+  public func definition() -> ModuleDefinition {
+    Name("ExpoBlueskyContextMenu")
+
+    View(ExpoBlueskyContextMenuView.self) {
+      Events(["onItemPress", "onPreviewPress"])
+
+      Prop("preview") { (view: ExpoBlueskyContextMenuView, value: [String: Any]?) in
+        view.setPreview(value)
+      }
+
+      Prop("menuItems") { (view: ExpoBlueskyContextMenuView, value: [[String: Any]]) in
+        view.setMenuItems(value)
+      }
+
+      Prop("borderRadius") { (view: ExpoBlueskyContextMenuView, value: Double) in
+        view.setBorderRadius(value)
+      }
+    }
+  }
+}