Add iOS share extension with rich link previews

- Implement share extension to receive URLs from other apps
- Display shared links with emoji indicator and rich preview cards
- Add custom compact link preview with image, title, and domain
- Configure app groups for data sharing between extension and main app
- Handle URL detection and parsing in share extension
- Update message formatting to show only emoji for shared links
- Add proper entitlements and activation rules for share extension

bitchat/ViewModels/ChatViewModel.swift

@@ -1498,8 +1498,34 @@ class ChatViewModel: ObservableObject {
             senderStyle.font = .system(size: 14, weight: .medium, design: .monospaced)
             result.append(sender.mergingAttributes(senderStyle))
             
-            // Process content with hashtags and mentions
-            let content = message.content
+            // Process content with hashtags, mentions, and markdown links
+            var content = message.content
+            
+            // First, check if content starts with 👇 followed by markdown link
+            if content.hasPrefix("👇 [") {
+                // This is a URL share - remove everything after the emoji
+                if let linkStart = content.firstIndex(of: "[") {
+                    let indexBeforeLink = content.index(before: linkStart)
+                    content = String(content[..<indexBeforeLink])
+                }
+            } else {
+                // Handle normal markdown links
+                let markdownLinkPattern = #"\[([^\]]+)\]\(([^)]+)\)"#
+                if let markdownRegex = try? NSRegularExpression(pattern: markdownLinkPattern, options: []) {
+                    let markdownMatches = markdownRegex.matches(in: content, options: [], range: NSRange(location: 0, length: content.count))
+                    
+                    // Process matches in reverse order to maintain string indices
+                    for match in markdownMatches.reversed() {
+                        if let fullRange = Range(match.range, in: content),
+                           let titleRange = Range(match.range(at: 1), in: content) {
+                            // Normal markdown link - replace with just the title
+                            let linkTitle = String(content[titleRange])
+                            content.replaceSubrange(fullRange, with: linkTitle)
+                        }
+                    }
+                }
+            }
+            
             let hashtagPattern = "#([a-zA-Z0-9_]+)"
             let mentionPattern = "@([a-zA-Z0-9_]+)"