Render descriptions with shared Markdown preview

Use one Markdown presentation for free-form content.

- issue and pull-request descriptions and comments
- milestone and commit descriptions

ios/Sources/DetailScreens.swift

@@ -1,5 +1,4 @@
 import Highlighter
-import MarkdownUI
 import QuickLook
 import SwiftUI
 import UIKit
@@ -402,7 +401,7 @@ private final class FileListView: UITableView, UITableViewDataSource, UITableVie
 private final class CommitHeaderView: UIView {
     private let stack = UIStackView()
     private let titleLabel = UILabel()
-    private let descriptionLabel = UILabel()
+    private var descriptionView: UIView?
     private let metadataStack = UIStackView()
 
     override init(frame: CGRect) {
@@ -414,9 +413,6 @@ private final class CommitHeaderView: UIView {
         titleLabel.adjustsFontForContentSizeCategory = true
         titleLabel.numberOfLines = 0
         titleLabel.accessibilityTraits = .header
-        descriptionLabel.font = .preferredFont(forTextStyle: .body)
-        descriptionLabel.adjustsFontForContentSizeCategory = true
-        descriptionLabel.numberOfLines = 0
 
         metadataStack.axis = .vertical
         metadataStack.spacing = 10
@@ -424,7 +420,6 @@ private final class CommitHeaderView: UIView {
         stack.spacing = 12
         stack.translatesAutoresizingMaskIntoConstraints = false
         stack.addArrangedSubview(titleLabel)
-        stack.addArrangedSubview(descriptionLabel)
         stack.addArrangedSubview(metadataStack)
         addSubview(stack)
         NSLayoutConstraint.activate([
@@ -440,8 +435,12 @@ private final class CommitHeaderView: UIView {
 
     func configure(_ page: CommitDetailsPage) {
         titleLabel.text = page.title
-        descriptionLabel.text = page.description
-        descriptionLabel.isHidden = page.description.isEmpty
+        descriptionView?.removeFromSuperview()
+        if !page.description.isEmpty {
+            let view = markdownView(page.description)
+            stack.insertArrangedSubview(view, at: 1)
+            descriptionView = view
+        }
         metadataStack.arrangedSubviews.forEach { $0.removeFromSuperview() }
         for metadata in page.metadata {
             let isCommit = metadata.label == "Commit"
@@ -1132,9 +1131,7 @@ struct RepositoryMarkdownPreview: View {
 
     var body: some View {
         ScrollView {
-            Markdown(source)
-                .markdownTheme(.gitHub)
-                .frame(maxWidth: .infinity, alignment: .leading)
+            MarkdownContent(source: source)
                 .padding()
         }
         .background(Color(uiColor: .systemBackground))
@@ -1235,6 +1232,7 @@ final class DiffViewController: UIViewController {
     }
 }
 
+@MainActor
 private func detailViews(
     title: String,
     state: String? = nil,
@@ -1285,6 +1283,7 @@ private func stateTitle(_ titleLabel: UILabel, state: String, subject: String) -
     return stack
 }
 
+@MainActor
 private func commentViews(
     _ comments: [CommentRow],
     editComment: ((CommentRow) -> Void)? = nil
@@ -1323,19 +1322,6 @@ private func commentViews(
     return views
 }
 
-private func markdownView(_ source: String) -> UITextView {
-    let view = UITextView()
-    view.attributedText = markdown(source)
-    view.isEditable = false
-    view.isSelectable = true
-    view.isScrollEnabled = false
-    view.backgroundColor = .clear
-    view.textContainerInset = .zero
-    view.textContainer.lineFragmentPadding = 0
-    view.adjustsFontForContentSizeCategory = true
-    return view
-}
-
 private func sectionLabel(_ text: String) -> UILabel {
     let label = UILabel()
     label.text = text