feat(ios): add share to support (#15340)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
  * Added iOS sharing for URLs, text, web pages, and images.
* Shared content can be reviewed, titled, and saved to an AFFiNE
workspace.
  * Choose destinations including workspaces, tags, and collections.
* Added previews, attachment handling, import status, retry support, and
success/error feedback.
* Pending shares are processed when AFFiNE opens or returns to the
foreground.
* **Bug Fixes**
* Improved workspace profile handling across different workspace types.
* Onboarding completion is now recorded immediately after successful
sign-in verification.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: DarkSky <25152247+darkskygit@users.noreply.github.com>

packages/frontend/apps/ios/App/ShareExtension/ShareViewController.swift

@@ -0,0 +1,89 @@
+//
+//  ShareViewController.swift
+//  ShareExtension
+//
+
+import SwiftUI
+import UIKit
+
+final class ShareViewController: UIViewController {
+  private let viewModel = ShareViewModel()
+  private var hostingController: UIHostingController<ShareExtensionView>?
+
+  override func viewDidLoad() {
+    super.viewDidLoad()
+    view.backgroundColor = .systemBackground
+
+    let rootView = ShareExtensionView(
+      viewModel: viewModel,
+      onCancel: { [weak self] in
+        self?.cancel()
+      },
+      onSave: { [weak self] in
+        self?.save()
+      }
+    )
+    let hosting = UIHostingController(rootView: rootView)
+    hostingController = hosting
+    addChild(hosting)
+    view.addSubview(hosting.view)
+    hosting.view.translatesAutoresizingMaskIntoConstraints = false
+    NSLayoutConstraint.activate([
+      hosting.view.topAnchor.constraint(equalTo: view.topAnchor),
+      hosting.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
+      hosting.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
+      hosting.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
+    ])
+    hosting.didMove(toParent: self)
+
+    Task {
+      await viewModel.load(from: extensionContext)
+    }
+  }
+
+  private func cancel() {
+    extensionContext?.completeRequest(returningItems: nil)
+  }
+
+  private func save() {
+    Task { [weak self] in
+      guard let self else { return }
+      let success = await viewModel.save()
+      guard success else { return }
+      _ = await openMainAppIfPossible()
+      extensionContext?.completeRequest(returningItems: nil, completionHandler: nil)
+    }
+  }
+
+  @discardableResult
+  private func openMainAppIfPossible() async -> Bool {
+    let url = ShareInboxConstants.openInboxURL
+    let openedByContext = await withCheckedContinuation { continuation in
+      extensionContext?.open(url) { success in
+        continuation.resume(returning: success)
+      } ?? continuation.resume(returning: false)
+    }
+    let opened = openedByContext || openMainAppViaResponderChain(url)
+    #if DEBUG
+      NSLog(
+        "[AFFiNE Share] open url=%@ extensionContext=%@ final=%@",
+        url.absoluteString,
+        openedByContext ? "YES" : "NO",
+        opened ? "YES" : "NO"
+      )
+    #endif
+    return opened
+  }
+
+  private func openMainAppViaResponderChain(_ url: URL) -> Bool {
+    var responder: UIResponder? = self
+    while let current = responder {
+      if let application = current as? UIApplication {
+        application.open(url, options: [:], completionHandler: nil)
+        return true
+      }
+      responder = current.next
+    }
+    return false
+  }
+}