perf: enable lazy loading for avatars and thumbnails

Added `loading="lazy"` and `decoding="async"` attributes to dynamically created `<img>` elements in:
- `js/historyView.js` (avatars)
- `js/ui/subscriptionHistoryController.js` (channel icons)
- `js/searchView.js` (added `decoding="async"`)
- `js/ui/profileModal/ProfileDirectMessageRenderer.js` (attachment previews, avatars)
- `js/ui/profileModalController.js` (attachment previews, saved profile avatars)

This reduces initial page load impact and bandwidth usage by deferring off-screen image loading.

Co-authored-by: PR0M3TH3AN <[email protected]>

js/ui/profileModal/ProfileDirectMessageRenderer.js

@@ -390,6 +390,8 @@ export class ProfileDirectMessageRenderer {
               img.src = result.objectUrl;
               img.alt = attachment.name || "Attachment preview";
               img.className = "h-40 w-full rounded-lg object-cover";
+              img.loading = "lazy";
+              img.decoding = "async";
               attachmentCard.appendChild(img);
             } else if (attachment.type?.startsWith("video/")) {
               const video = document.createElement("video");
@@ -884,6 +886,8 @@ export class ProfileDirectMessageRenderer {
     avatarImg.className = "h-full w-full object-cover";
     avatarImg.src = avatarUrl;
     avatarImg.alt = `${safeName} avatar`;
+    avatarImg.loading = "lazy";
+    avatarImg.decoding = "async";
     avatarWrapper.appendChild(avatarImg);
 
     const textStack = document.createElement("div");