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/main-content/view/subcomponents/MainContentTitle.tsx

@@ -70,7 +70,7 @@ export default function MainContentTitle({
       <div className="min-w-0 flex-1">
         {activeTab === 'chat' && selectedSession ? (
           <div className="min-w-0">
-            <h2 className="scrollbar-hide overflow-x-auto whitespace-nowrap text-sm font-semibold leading-tight text-foreground">
+            <h2 className="truncate text-sm font-semibold leading-tight text-foreground">
               {getSessionTitle(selectedSession)}
             </h2>
             <div className="truncate text-[11px] leading-tight text-muted-foreground">{selectedProject.displayName}</div>