[codex] Match blog pages to academic homepage tone

[Ridealist]

Summary

• Add scoped academic tone overrides for blog, category, archive, sidebar, table of contents, footer, and dark mode surfaces.
• Align sidebar profile links and structured social metadata with the homepage profile links.
• Move the Academicons stylesheet into the shared head so Scholar and CV icons render across homepage and blog pages.

Impact

• Blog and category pages now visually follow the new academic homepage tone without replacing Minimal Mistakes or changing permalink behavior.
• Sidebar profile links no longer show stale Twitter or placeholder social entries.
• Home, archive, and post pages share the same Scholar and CV icon source.

Closes #21

Validation

• bundle exec jekyll build
• bundle exec jekyll build --safe
• Verified 200 responses for /, /llm/, /hci/, /datascience/, /isd/, /categories/, /isd/problem-analysis/, and /llm/fine-tuning-llm/.
• Captured Playwright screenshots with local Chrome for /llm/ desktop, /isd/problem-analysis/ mobile, and /categories/ dark mode.