feat(chat): add Ctrl+Enter shortcut to send messages

Allows users to send messages using Ctrl+Enter (or Cmd+Enter on Mac)
in addition to the existing Enter key shortcut.

src/components/editor/MentionEditor.tsx

@@ -216,8 +216,11 @@ export const MentionEditor = forwardRef<
             "prose prose-sm max-w-none focus:outline-none min-h-[2rem] px-3 py-1.5",
         },
         handleKeyDown: (view, event) => {
-          // Submit on Enter (without Shift)
-          if (event.key === "Enter" && !event.shiftKey) {
+          // Submit on Enter (without Shift) or Ctrl/Cmd+Enter
+          if (
+            event.key === "Enter" &&
+            (!event.shiftKey || event.ctrlKey || event.metaKey)
+          ) {
             event.preventDefault();
             // Get editor from view state
             const editorInstance = (view as any).editor;