fix: exclude embed thumbnails from image context menu actions

Add data-embed-thumbnail marker to VideoEmbed, GenericEmbed, and
RichEmbed thumbnail containers. Update detection logic to skip
these alongside avatars. Also remove redundant filename derivation
in Save Image menu item.

packages/web/src/components/chat/Message.tsx

@@ -173,9 +173,9 @@ export function Message({ message, isCompact, isFirstInGroup, previousMessageId
     e.stopPropagation();
     const selectedText = window.getSelection()?.toString() ?? '';
 
-    // Detect if the right-click target is a content image (not an avatar)
+    // Detect if the right-click target is a content image (not an avatar or embed thumbnail)
     const imgEl = (e.target as HTMLElement).closest('img') as HTMLImageElement | null;
-    const isContentImage = imgEl && !imgEl.closest('[data-avatar]');
+    const isContentImage = imgEl && !imgEl.closest('[data-avatar]') && !imgEl.closest('[data-embed-thumbnail]');
     const imageUrl = isContentImage ? imgEl.src : null;
 
     const items = buildMessageMenuItems({

packages/web/src/components/chat/embeds/GenericEmbed.tsx

@@ -41,7 +41,7 @@ export function GenericEmbed({ embed }: GenericEmbedProps) {
         )}
       </div>
       {embed.image && (
-        <div className="w-[80px] h-[80px] m-3 flex-shrink-0">
+        <div data-embed-thumbnail className="w-[80px] h-[80px] m-3 flex-shrink-0">
           <img
             src={embed.image}
             alt=""

packages/web/src/components/chat/embeds/RichEmbed.tsx

@@ -50,7 +50,7 @@ export function RichEmbed({ embed }: RichEmbedProps) {
         >
           <div className="flex items-start gap-3 p-3">
             {embed.image && (
-              <div className="w-[80px] h-[80px] flex-shrink-0">
+              <div data-embed-thumbnail className="w-[80px] h-[80px] flex-shrink-0">
                 <img
                   src={embed.image}
                   alt=""

packages/web/src/components/chat/embeds/VideoEmbed.tsx

@@ -45,6 +45,7 @@ export function VideoEmbed({ embed }: VideoEmbedProps) {
         ) : (
           <button
             type="button"
+            data-embed-thumbnail
             onClick={() => setIsPlaying(true)}
             className="absolute inset-0 w-full h-full flex items-center justify-center group focus:outline-none"
             aria-label={`Play ${embed.title ?? 'video'}`}

packages/web/src/components/chat/messageMenuItems.tsx

@@ -55,10 +55,7 @@ export function buildMessageMenuItems(params: MessageMenuParams): ContextMenuIte
           <path d="M19 9h-4V3H9v6H5l7 7 7-7zM5 18v2h14v-2H5z" />
         </svg>
       ),
-      onClick: () => {
-        const filename = imageUrl.split('/').pop()?.split('?')[0] ?? 'image';
-        saveImage(imageUrl, filename);
-      },
+      onClick: () => saveImage(imageUrl),
     });
     items.push({
       key: 'copy-image',