Frontend review and design revision

[maxine-at-forecast]

Review the current server-rendered frontend (Jinja2 + HTMX + PicoCSS) and revise the design for improved usability and visual polish.

Scope

• Audit all existing pages: home/search, dataset detail, schema detail, schemas list, publisher profile, and about
• Identify UX issues: navigation flow, information hierarchy, responsiveness, accessibility
• Revise visual design: typography, spacing, color palette, component consistency
• Improve mobile responsiveness
• Review HTMX interactions for smoothness and loading states

Context

The frontend was added in v0.2.0b1 as a lightweight dataset browser. It uses:

• Jinja2 templates in src/atdata_app/templates/
• HTMX for dynamic interactions
• PicoCSS as the base stylesheet
• Routes gated to the frontend hostname (not served on the API subdomain)