Update summarize comments UI

What does this MR do and why?

Update summarize comments UI

• Add card header
  • Added tanuki (just because it seems to be everywhere; happy to remove it if it's used incorrectly)
  • Added AI-generated... in title; matches the ai generated test cases drawer
• Remove footer border
• Removed "Text generated by AI" from footer because it's also in the header
• (not in screenshots) Updates button text from See summary to View summary (suggested by @sselhorn in !121574 (comment 1402324156))
• Add feedback link (removed until we have a public feedback issue)

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Feature.enable(:summarize_comments)
• Look at issue with comments
• Click View summary at top of activity feed

#411677 (closed)