fix(ui): wrap "Add to chat" selections in md fenced blocks (#641) (#684)

packages/ui/src/components/chat/message/TextSelectionMenu.tsx
  - What: Wrap selectedText in ```md fenced block before appending to composer.
  - Why: Selections were appended as raw inline text with no visual distinction.

packages/ui/src/components/chat/ChatInput.tsx
  - What: Replace trimEnd()/trim() + single-space join with raw prev + \n\n separator in append branch.
  - Why: Existing composer newlines were being destroyed and multiple appends ran together.

packages/ui/src/components/session/ProjectNotesTodoPanel.tsx
  - What: Wrap todoText in ```md fenced block before appending to composer.
  - Why: Todo text sent to current session should have the same fenced formatting.

packages/ui/src/components/session/ProjectNotesTodoPanel.tsx

@@ -192,7 +192,8 @@ export const ProjectNotesTodoPanel: React.FC<ProjectNotesTodoPanelProps> = ({
         return;
       }
       routeToChat();
-      setPendingInputText(todoText, 'append');
+      const fenced = `\`\`\`md\n${todoText}\n\`\`\``;
+      setPendingInputText(fenced, 'append');
       toast.success('Todo sent to current session');
       onActionComplete?.();
     },