Merge upstream/experimental into feat/citations

Resolved conflicts:
- backend/src/gateway/routers/artifacts.py: Keep citations block removal for markdown downloads
- frontend/src/components/workspace/messages/message-list-item.tsx: Keep improved citation handling with rehypePlugins, humanMessagePlugins, and CitationsLoadingIndicator

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/core/i18n/locales/en-US.ts

@@ -79,7 +79,12 @@ export const enUS: Translations = {
     proMode: "Pro",
     proModeDescription:
       "Reasoning, planning and executing, get more accurate results, may take more time",
+    ultraMode: "Ultra",
+    ultraModeDescription:
+      "Pro mode with subagents enabled, maximum capability for complex multi-step tasks",
     searchModels: "Search models...",
+    surpriseMe: "Surprise",
+    surpriseMePrompt: "Surprise me",
     suggestions: [
       {
         suggestion: "Write",
@@ -214,7 +219,7 @@ export const enUS: Translations = {
       tools: "Tools",
       skills: "Skills",
       notification: "Notification",
-      acknowledge: "Acknowledge",
+      about: "About",
     },
     memory: {
       title: "Memory",