Add Utumishi static archive landing page (index, styles, README)

[t-mwau]

Motivation

• Provide a lightweight, responsive static landing page to present journals, books, and learning materials without a framework or build step.
• Ship a self-contained example that can be dropped into DecodeLabs-Internship/utumishi/ for quick local serving and review.

Description

• Add index.html which implements the archive landing page markup including a hero, collections, archive workflow, services, and contact/footer.
• Add css/styles.css with theme variables, responsive layout, mobile navigation toggle, and styles for cards, grids, and the archive panel.
• Add utumishi/README.md describing repository placement, recommended file layout, local run instructions (python3 -m http.server 8000 --directory utumishi) and notes about the remote hero image.

Testing

• No automated tests were added or executed for this static HTML/CSS update.

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Codex Task