Prompt

Build a blog index page (a single self-contained `index.html` with inline CSS, no frameworks)
for a publication called "Field Notes".

Include: a header with the publication name and nav; a responsive grid of six article cards,
each with a cover image, a category tag, a headline, a one-line excerpt, and an author + date
line; and a footer. The grid should reflow gracefully from desktop to mobile.

Put the whole page in one HTML code block.