perf(images): add loading=lazy to in-list previews and attachments

Four image sites that render thumbnails/previews inside lists or tab
panels now hint loading=lazy so the browser defers the network fetch
until the element is near the viewport:
- Support.tsx attachment preview grid
- AdminTickets.tsx reply attachment grid
- BroadcastPreview.tsx photo preview
- BrandingTab.tsx logo preview in admin settings

Top-of-page logos (AppHeader/AppShell/DesktopSidebar/Login/Telegram
redirect/DeepLink) intentionally stay eager — they're above the fold
and should paint on first frame. Payment-method icons (6x6 px) are
already negligible. Compose attachment previews use blob: URLs where
loading=lazy is a no-op.

src/pages/Support.tsx

@@ -337,6 +337,7 @@ export default function Support() {
               <img
                 src={att.preview}
                 alt="Preview"
+                loading="lazy"
                 className="h-16 w-16 rounded-lg border border-dark-700 object-cover"
               />
             ) : (