Suggestion cards in nested lists

We have in the past encouraged suggestion lists inside of nested lists (e.g. querychat) and might want to support suggestion cards in this context, e.g.

Here are a few ideas to get you started:

* **Analyze the data**
  * <span class="suggestion">What is the average body mass of the penguins?</span>
  * <span class="suggestion">How many species are in this dataset?</span>
* **Create visualizations**
  * <span class="suggestion">Show me a bar chart of penguin counts by species.</span>
  * <span class="suggestion">Plot a scatter plot of bill length vs. bill depth.</span>
* **Filter and sort records**
  * <span class="suggestion">Show me all penguins from the Biscoe island.</span>
  * <span class="suggestion">Sort the penguins by flipper length, largest to smallest.</span>

Originally posted by @cpsievert in https://github.com/posit-dev/shinychat/issues/219#issuecomment-4452870571

Start by reproducing the nested-list Markdown example from the issue in the shinychat UI and inspect how suggestion cards are currently detected and rendered. Done means suggestions inside nested lists render as cards while existing suggestion-list behavior continues to work.