Update assistant entry points

[ethanpalm]

Documentation changes

This PR documents the new assistant entry point of highlighting text snippets, adds the missing ask AI on code blocks, and reformats the list of entry points into H3 sections.

Closes https://linear.app/mintlify/issue/DOC-211/document-new-ask-ai-entry-points

---

For Reviewers

When reviewing documentation PRs, please consider:

✅ Technical accuracy

• Code examples work as written
• Commands and configurations are correct
• Links resolve to the right destinations
• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
• Steps are in logical order
• Nothing important is missing
• Examples help illustrate the concepts

✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed
• Error messages or troubleshooting guidance is helpful

---

Note

Documents new assistant entry points and UI placement, restructures usage guidance, and updates model reference to Claude Opus 4.5.

• Docs – Use the assistant:
  • Reorganize usage into H3 sections with clearer structure.
  • Add UI placement section (button vs. bottom bar) with images.
  • Add new entry points: Highlight text → Add to assistant and Ask AI on code blocks.
  • Clarify keyboard shortcut and URL parameter entry points.
• About:
  • Update model reference to Claude Opus 4.5.
• Headings:
  • Tweak titles to Configure the assistant and Use the assistant.
• Misc:
  • Minor whitespace cleanup in a note.

^{Written by Cursor Bugbot for commit acfe05a. This will update automatically on new commits. Configure here.}