Add iOS Share Extension support

- Create share extension to handle shared content from other apps
- Support sharing text, URLs, and prepare for future image support
- Use app groups for data sharing between extension and main app
- Add URL scheme handling for app communication
- Add entitlements for app groups
- Display system message when content is shared
- Update project configuration to include share extension

bitchat/BitchatApp.swift

@@ -26,6 +26,14 @@ struct BitchatApp: App {
                 .environmentObject(chatViewModel)
                 .onAppear {
                     NotificationDelegate.shared.chatViewModel = chatViewModel
+                    #if os(iOS)
+                    appDelegate.chatViewModel = chatViewModel
+                    #endif
+                    // Check for shared content
+                    checkForSharedContent()
+                }
+                .onOpenURL { url in
+                    handleURL(url)
                 }
         }
         #if os(macOS)
@@ -33,10 +41,57 @@ struct BitchatApp: App {
         .windowResizability(.contentSize)
         #endif
     }
+    
+    private func handleURL(_ url: URL) {
+        if url.scheme == "bitchat" && url.host == "share" {
+            // Handle shared content
+            checkForSharedContent()
+        }
+    }
+    
+    private func checkForSharedContent() {
+        // Check app group for shared content from extension
+        guard let userDefaults = UserDefaults(suiteName: "group.chat.bitchat"),
+              let sharedContent = userDefaults.string(forKey: "sharedContent"),
+              let sharedDate = userDefaults.object(forKey: "sharedContentDate") as? Date else {
+            return
+        }
+        
+        // Only process if shared within last 30 seconds
+        if Date().timeIntervalSince(sharedDate) < 30 {
+            let contentType = userDefaults.string(forKey: "sharedContentType") ?? "text"
+            
+            // Clear the shared content
+            userDefaults.removeObject(forKey: "sharedContent")
+            userDefaults.removeObject(forKey: "sharedContentType")
+            userDefaults.removeObject(forKey: "sharedContentDate")
+            userDefaults.synchronize()
+            
+            // Show notification about shared content
+            DispatchQueue.main.async {
+                // Add system message about sharing
+                let systemMessage = BitchatMessage(
+                    sender: "system",
+                    content: "preparing to share \(contentType)...",
+                    timestamp: Date(),
+                    isRelay: false
+                )
+                self.chatViewModel.messages.append(systemMessage)
+            }
+            
+            // Send the shared content after a short delay
+            DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
+                let prefix = contentType == "url" ? "Shared link: " : ""
+                self.chatViewModel.sendMessage(prefix + sharedContent)
+            }
+        }
+    }
 }
 
 #if os(iOS)
 class AppDelegate: NSObject, UIApplicationDelegate {
+    weak var chatViewModel: ChatViewModel?
+    
     func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
         return true
     }