Add Share Extension for importing recipes via URL

Adds a Share Extension so users can share URLs from Safari (or any app)
to open the main app with the ImportURLSheet pre-filled. Uses a custom
URL scheme (nextcloud-cookbook://) as the bridge between the extension
and the main app.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

ShareExtension/Info.plist

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>NSExtension</key>
+	<dict>
+		<key>NSExtensionAttributes</key>
+		<dict>
+			<key>NSExtensionActivationRule</key>
+			<dict>
+				<key>NSExtensionActivationSupportsWebURLWithMaxCount</key>
+				<integer>1</integer>
+			</dict>
+		</dict>
+		<key>NSExtensionPointIdentifier</key>
+		<string>com.apple.share-services</string>
+		<key>NSExtensionPrincipalClass</key>
+		<string>$(PRODUCT_MODULE_NAME).ShareViewController</string>
+	</dict>
+</dict>
+</plist>