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/ShareViewModel.swift

@@ -0,0 +1,93 @@
+import Foundation
+import UIKit
+
+@MainActor
+final class ShareViewModel: ObservableObject {
+  @Published var title = ""
+  @Published var previewText = ""
+  @Published var previewImage: UIImage?
+  @Published var isLoading = true
+  @Published var isSaving = false
+  @Published var hasSaved = false
+  @Published var errorMessage: String?
+
+  var actionTitle: String {
+    "Open AFFiNE"
+  }
+
+  var canSave: Bool {
+    !isLoading
+      && !isSaving
+      && !title.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
+      && draft?.content != nil
+  }
+
+  private var draft: SharePayloadDraft?
+  private let store: ShareInboxStore
+
+  init(store: ShareInboxStore = .shared) {
+    self.store = store
+  }
+
+  func load(from extensionContext: NSExtensionContext?) async {
+    isLoading = true
+    defer { isLoading = false }
+
+    let items = extensionContext?.inputItems.compactMap { $0 as? NSExtensionItem } ?? []
+    let built = await SharePayloadBuilder.build(from: items)
+    draft = built
+    title = built.title
+    previewText = built.previewText
+    errorMessage = built.errorMessage
+    if let file = built.file {
+      previewImage = UIImage(data: file.data)?
+        .preparingThumbnail(of: CGSize(width: 480, height: 480))
+    }
+  }
+
+  func save() async -> Bool {
+    guard !isSaving, !hasSaved else { return false }
+    isSaving = true
+    defer { isSaving = false }
+
+    let trimmedTitle = title.trimmingCharacters(in: .whitespacesAndNewlines)
+    guard !trimmedTitle.isEmpty else {
+      errorMessage = "Title is required."
+      return false
+    }
+    guard let draft, let content = draft.content else {
+      errorMessage = draft?.errorMessage ?? "Nothing to share."
+      return false
+    }
+
+    let itemId = UUID().uuidString
+    var attachments: [ShareInboxAttachment] = []
+    var attachmentData: [(ShareInboxAttachment, Data)] = []
+    if let file = draft.file {
+      let attachment = ShareInboxAttachment(
+        fileName: file.fileName,
+        mimeType: file.mimeType,
+        relativePath: "\(itemId)/\(file.fileName)"
+      )
+      attachments = [attachment]
+      attachmentData = [(attachment, file.data)]
+    }
+
+    let item = ShareInboxItem(
+      id: itemId,
+      title: trimmedTitle,
+      content: content,
+      previewText: draft.previewText,
+      attachments: attachments
+    )
+
+    do {
+      try store.enqueue(item, attachmentData: attachmentData)
+      hasSaved = true
+      return true
+    } catch {
+      errorMessage = "Failed to save shared content."
+      return false
+    }
+  }
+}