Polish nav, transitions, layout, SEO, a11y, LaTeX, and Lighthouse CI

Nav bar & layout consistency
- Base.astro's `wide` layout now defaults on for every page (was opt-in),
  fixing the nav bar wrapping differently depending on page width
- Icon buttons for search and theme toggle (magnifying glass, sun/moon),
  replacing the plain "Search" text link and the "◐" glyph
- Search is now a Cmd/Ctrl+K modal over Pagefind (lazy-loaded on first
  open) instead of a separate /search/ page, matching the old site
- Fixed the article page's TOC sitting with unwanted left padding relative
  to the header (grid was center-justified instead of start-justified)

Smooth navigation
- Added Astro's ClientRouter for animated page transitions
- Every page-local script that only ran once at module load (three.js
  hero, minimap, comments, book-spine carousel, scroll-to-top, reading
  progress, theme toggle, Pagefind init) now re-initializes via
  astro:page-load, with AbortController-based cleanup so window/document
  listeners don't accumulate across client-side navigations

Restored from the legacy Zola site
- Reading progress bar (article pages) and scroll-to-top button
- Share buttons (X, Bluesky, LinkedIn, Reddit, HN, email) on writings
- Prev/next post navigation with the old label/title layout
- Utterances comments, wired to andwati/andwati.com with dark/light
  theme sync
- YouTube embeds: any plain <iframe src="...youtube-nocookie.com...">
  is now auto-wrapped in a responsive 16:9 container, gets
  loading="lazy", and emits VideoObject JSON-LD — no shortcode needed
- LaTeX: $inline$ and $$block$$ math renders to static HTML via KaTeX at
  build time (no client-side JS shipped for it)
- Tags page redesigned as a centered, alphabetical tag cloud

Removed the related-posts section per request.

Accessibility & contrast
- --accent (#d1502f) measured 4.0:1 on the light background, just under
  WCAG AA's 4.5:1 for normal text — darkened to #a84025 (5.7:1), plus
  matching light-mode-only fixes for the two hljs syntax colors and the
  tip/warning callout colors that had the same problem in light mode
- Fixed heading-order violations (h1 straight to h3 with nothing at h2)
  across the homepage, writings/portfolio/bookshelf/blogs lists, and tag
  pages — introduced a shared .entry-title class for the h2 list titles
- Fixed inconsistent title-link underline colors: a plain <a> carries its
  own default underline (in its own text color) instead of matching its
  parent heading's accent-colored one — h1/h2/h3 anchors now explicitly
  inherit the heading's decoration
- Bookshelf spine colors are generated per-title from a hash; the
  lightness-based text-color heuristic could still produce sub-4.5:1
  contrast for some hues (e.g. green) — now computes real WCAG contrast
  and adjusts

Performance
- The three.js homepage hero was the single largest main-thread cost
  site-wide (dragging that page's Lighthouse performance score to the low
  80s while every other page scored 95+): three.js is now dynamically
  imported only once the browser is idle (WebGL-support check split into
  its own tiny module so unsupported browsers never fetch it at all), the
  render loop is capped to ~30fps, and hover raycasting only runs on an
  actual pointer move instead of every frame

SEO & structured data
- Self-referential canonical links site-wide (with override support for
  posts first published elsewhere)
- Sitewide WebSite/Person JSON-LD, plus per-article BlogPosting,
  BreadcrumbList, and (when applicable) VideoObject JSON-LD
- robots.txt explicitly welcomes AI/LLM crawlers (GPTBot, ClaudeBot,
  PerplexityBot, Google-Extended, CCBot, etc.) and points at llms.txt
- Added an Atom feed (RSS and JSON Feed already existed)
- Sitemap now sets <lastmod> per entry from its own date/updated
  frontmatter instead of leaving every URL at build time

Analytics & comments infra
- Self-hosted Umami wiring via PUBLIC_UMAMI_SCRIPT_URL/WEBSITE_ID
  (apps/site/.env.example), no-ops until both are set
- sws.toml's CSP updated to allow utteranc.es and analytics.andwati.com —
  without this both were silently blocked in production

Lighthouse CI
- @lhci/cli wired up against the built site (mobile + desktop configs),
  `pnpm run lighthouse`, and a GitHub Actions workflow to run it on every
  push/PR — reporting only for now, no failing thresholds

content/README.md

@@ -104,3 +104,15 @@ feed_url = "https://.../rss.xml"
 
 Body is a one-to-two sentence blurb on why you follow it. No live feed
 fetching — this list is hand-curated and static.
+
+## Markdown extras (all body content)
+
+- **LaTeX**: `$inline$` and `$$block$$` math renders to static HTML/MathML
+  at build time (`marked-katex-extension` in `toml-content-loader.ts`) — no
+  client-side JS shipped for it.
+- **Callouts**: `{% <note> %} ... {% </note> %}` (also `tip`/`warning`/
+  `danger`) renders as a styled callout box.
+- **YouTube embeds**: paste a plain `<iframe src="https://www.youtube-
+  nocookie.com/embed/VIDEO_ID" ...></iframe>` — it's automatically wrapped
+  in a responsive 16:9 container, gets `loading="lazy"`, and emits
+  `VideoObject` structured data. No shortcode needed.