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/Info.plist

@@ -40,5 +40,16 @@
 	<array>
 		<string>UIInterfaceOrientationPortrait</string>
 	</array>
+	<key>CFBundleURLTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleURLSchemes</key>
+			<array>
+				<string>bitchat</string>
+			</array>
+			<key>CFBundleURLName</key>
+			<string>chat.bitchat</string>
+		</dict>
+	</array>
 </dict>
 </plist>