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/ShareViewController.swift

@@ -0,0 +1,79 @@
+//
+//  ShareViewController.swift
+//  ShareExtension
+//
+//  Created by Hendrik Hogertz on 15.02.26.
+//
+
+import UIKit
+import UniformTypeIdentifiers
+
+class ShareViewController: UIViewController {
+
+    override func viewDidAppear(_ animated: Bool) {
+        super.viewDidAppear(animated)
+        handleSharedItems()
+    }
+
+    private func handleSharedItems() {
+        guard let extensionItems = extensionContext?.inputItems as? [NSExtensionItem] else {
+            completeRequest()
+            return
+        }
+
+        for item in extensionItems {
+            guard let attachments = item.attachments else { continue }
+            for provider in attachments {
+                if provider.hasItemConformingToTypeIdentifier(UTType.url.identifier) {
+                    provider.loadItem(forTypeIdentifier: UTType.url.identifier) { [weak self] item, _ in
+                        if let url = item as? URL {
+                            self?.openMainApp(with: url.absoluteString)
+                        } else {
+                            self?.completeRequest()
+                        }
+                    }
+                    return
+                } else if provider.hasItemConformingToTypeIdentifier(UTType.plainText.identifier) {
+                    provider.loadItem(forTypeIdentifier: UTType.plainText.identifier) { [weak self] item, _ in
+                        if let text = item as? String, let url = URL(string: text), url.scheme?.hasPrefix("http") == true {
+                            self?.openMainApp(with: url.absoluteString)
+                        } else {
+                            self?.completeRequest()
+                        }
+                    }
+                    return
+                }
+            }
+        }
+
+        completeRequest()
+    }
+
+    private func openMainApp(with urlString: String) {
+        guard let encoded = urlString.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed),
+              let appURL = URL(string: "nextcloud-cookbook://import?url=\(encoded)")
+        else {
+            completeRequest()
+            return
+        }
+
+        // Use the responder chain to open the URL
+        var responder: UIResponder? = self
+        while let r = responder {
+            if let application = r as? UIApplication {
+                application.open(appURL, options: [:], completionHandler: nil)
+                break
+            }
+            responder = r.next
+        }
+
+        // Give the system a moment to process the URL before dismissing
+        DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) { [weak self] in
+            self?.completeRequest()
+        }
+    }
+
+    private func completeRequest() {
+        extensionContext?.completeRequest(returningItems: nil)
+    }
+}