[site] Fix docs latest notice and Blogs label

[xxubai]

Why are the changes needed?

The docs site currently has two user-facing issues:

• The docs top navigation renders Blogs as lowercase blogs.
• The latest documentation does not clearly indicate that it reflects unreleased development changes, which can confuse users looking for stable docs.

N/A (no linked issue).

Brief change log

• Capitalize the Blogs entry in the docs top navigation.
• Add a latest-only banner that explains the page reflects unreleased development documentation.
• Link the banner to the current stable docs version and style it to stand out without overwhelming the page.

How was this patch tested?

• Add some test cases that check the changes thoroughly including negative and positive cases if possible
• Add screenshots for manual tests if appropriate
• Run test locally before making a pull request (hugo -b http://127.0.0.1:1314/docs/latest/ -d public in site/amoro-docs)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)