fix: release a queued message once an attached URL finishes (#28381)

A message sent while an attachment is still uploading is held in the chat
queue until the file settles. For files that release works, because the
message input calls onUpdate once the upload completes, which refreshes the
queued entry and asks the queue to run.

Attaching a URL takes a different path. uploadWeb sets the item to uploaded
but calls neither onUpdate nor processNextInQueue, and the queue is
otherwise only revisited when a generation finishes or when the chat is
mounted while idle. In a new chat with nothing generating, none of those
happen, so a message queued behind a URL waits with no event able to
release it until the chat is reloaded.

uploadWeb now asks the queue to run when it is done, the same way the file
path already does.

src/lib/components/chat/Chat.svelte

@@ -1605,6 +1605,8 @@
 				toast.error(`${e}`);
 			}
 		}
+
+		await onUpdate();
 	};
 
 	const onUpdate = async ({ file }: { file?: any } = {}) => {