Improve usefulness of summary

[cjcenizal]

We can make the summary more useful in a few ways.

Formatting

We currently render the response in plain text. We can enhance this with Markdown support so we can:

• Emphasize important terms or topics by bolding them.
• Group items into unordered lists and enumerate steps with ordered lists.
• Render URLs as clickable links.

Simplifying references

We currently cross-reference the grounding data with inline citations. If there is link information in these results, we can distill this information down into clickable URLs which we can either list below the summary or surface as clickable inline links within the summary.

CC @ofermend

[cjcenizal]

The formatting item has been addressed by #95