fix(chat): header ellipsis, Codex logo on light theme, portal copy menu

- MainContentTitle: truncate the session title with an ellipsis instead
  of horizontal-scrolling it
- MessageComponent: use text-foreground for the provider logo chip so the
  currentColor Codex/OpenAI mark is visible on the light theme
- MessageCopyControl: render the copy-format dropdown in a portal so it
  escapes the chat message's `contain: paint` clip box; anchor it to the
  trigger, flip above near the viewport bottom, close on scroll/resize

src/components/chat/view/subcomponents/MessageComponent.tsx

@@ -166,7 +166,7 @@ const MessageComponent = memo(({ message, prevMessage, createDiff, onFileOpen, a
                   🔧
                 </div>
               ) : (
-                <div className="flex h-8 w-8 flex-shrink-0 items-center justify-center rounded-full p-1 text-sm text-white">
+                <div className="flex h-8 w-8 flex-shrink-0 items-center justify-center rounded-full p-1 text-sm text-foreground">
                   <SessionProviderLogo provider={provider} className="h-full w-full" />
                 </div>
               )}