Image Lazy Loading & Enhanced Loading Experience (#1230)

* LoadingView and Image Lazy Loading
- Add an X button to Loading View to allow exiting out of V spinner view early. Appears after 3 second delay (not shown when loading completes in timely manner). Shows for thread loading only i.e. Does not show for new post previews or private message loading.
- Timeouts added to image loading. In case of failure set "Dead Image" badge similar to Dead Tweets
- Fix ghost lottie loading by using locally provided lottie.js file.
- iOS 15.4+ now accepts the loading="lazy" attribute. Using this for image element lazy loading. Tweets use IntersectionObserver method.
- Added a retry option to Dead Tweet badge, similar to Dead Image badge

Author: dfsm

App/Misc/HTMLRenderingHelpers.swift

@@ -6,6 +6,17 @@ import HTMLReader
 
 extension HTMLDocument {
 
+    // MARK: - Constants
+
+    /// Number of post images to load immediately before deferring to lazy loading.
+    /// IMPORTANT: This value must match IMMEDIATELY_LOADED_IMAGE_COUNT constant in RenderView.js
+    private static let immediatelyLoadedImageCount = 10
+
+    /// 1x1 transparent GIF used as placeholder for lazy-loaded images
+    private static let transparentPixelPlaceholder = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"
+
+    // MARK: - HTML Processing Methods
+
     /// Finds links that appear to be to Bluesky posts and adds a `data-bluesky-post` attribute to those links.
     func addAttributeToBlueskyLinks() {
         for a in nodes(matchingSelector: "a[href *= 'bsky.app']") {
@@ -138,22 +149,56 @@ extension HTMLDocument {
      - Turns all non-smiley `<img src=>` elements into `<a data-awful='image'>src</a>` elements (if linkifyNonSmiles == true).
      - Adds .awful-smile to smilie elements.
      - Rewrites URLs for some external image hosts that have changed domains and/or URL schemes.
+     - Defers loading of post content images beyond the first 10 (lazy loading).
      */
     func processImgTags(shouldLinkifyNonSmilies: Bool) {
+        var postContentImageCount = 0
+
         for img in nodes(matchingSelector: "img") {
             guard
                 let src = img["src"],
                 let url = URL(string: src)
                 else { continue }
-            
+
             let isSmilie = isSmilieURL(url)
-            
+
             if isSmilie {
                 img.toggleClass("awful-smile")
-            } else if let postimageURL = fixPostimageURL(url) {
-                img["src"] = postimageURL.absoluteString
-            } else if let waffleURL = randomwaffleURLForWaffleimagesURL(url) {
-                img["src"] = waffleURL.absoluteString
+            } else {
+                // Check if this is an avatar (has class="avatar")
+                let isAvatar = img["class"]?.contains("avatar") ?? false
+
+                // Skip attachment.php files (require auth, handled elsewhere)
+                let isAttachment = url.lastPathComponent == "attachment.php"
+
+                // Apply URL fixes first to get the final URL
+                var finalURL = src
+                if let postimageURL = fixPostimageURL(url) {
+                    finalURL = postimageURL.absoluteString
+                } else if let waffleURL = randomwaffleURLForWaffleimagesURL(url) {
+                    finalURL = waffleURL.absoluteString
+                }
+
+                // Check if this is a data: URI (inline data that shouldn't be lazy-loaded)
+                let isDataURI = finalURL.starts(with: "data:")
+
+                // Determine whether to load immediately or defer based on image type and count
+                if !isAvatar && !isAttachment && !isDataURI {
+                    // This is a post content image (not avatar, not smilie, not attachment)
+                    postContentImageCount += 1
+
+                    if postContentImageCount > Self.immediatelyLoadedImageCount {
+                        // Defer loading for images beyond the immediately loaded count (browser handles lazy loading)
+                        img["loading"] = "lazy"
+                        img["src"] = finalURL
+                    } else {
+                        // Load immediately
+                        img["src"] = finalURL
+                    }
+                } else {
+                    // Avatars, attachments, and data URIs always load immediately
+                    img["src"] = finalURL
+                }
             }
 
             if shouldLinkifyNonSmilies, !isSmilie {