Update CLI docs for mint update

[ethanpalm]

Documentation changes

This PR updates our docs to use mint update for keeping the CLI up to date with the client.

• General improvements to https://mintlify.com/docs/installation
  • Renames to CLI since it's about more than installation
  • Uses <Steps> for the procedure
  • Adds mint update to the updates section
  • Updates the yarn update code sample
  • Copyediting for the rest of the content in this article
• Edits https://mintlify.com/docs/changelog#npm-i-mint to recommend mint update over npm-i-mint

I didn't document mint upgrade since our docs generally avoid any mention of mint.json, so people shouldn't need to use that command frequently. But could add it in to document all commands.

Closes https://linear.app/mintlify/issue/DOC-62/update-cli-docs

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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

[hahnbeelee]

left some comments - otherwise LGTM