feat: implement design system — domain colors, date typography, interaction states, CV family colors

Apply the collaboratively-written design system from .interface-design/system.md:

- Domain color map: Social pages (rose), Code pages (emerald), Reading pages
  (orange), Music pages (purple) replace generic accent tokens
- Font-mono on all <time> elements via global CSS rule + wrap 7 non-<time> dates
- Shadow standardization: replace hover:shadow-lg with border-hover on news cards
- Active states: scale(0.97) press feedback on buttons and pagination links
- Gradient cleanup: remove to-white gradient on github featured project cards
- CV Skills & Interests: cycle through 8 distinct colors per family category
  (amber, emerald, sky, rose, purple, orange, teal, indigo) on both CV page
  and homepage
- Update system.md with refined palette documentation and domain color spec

Files: 19 changed across templates, CSS, and design documentation

Confab-Link: http://localhost:8080/sessions/bd3f7012-c703-47e9-bfe2-2ad04ce1842d

digest.njk

@@ -18,7 +18,7 @@ permalink: "digest/{{ digest.slug }}/"
     {{ digest.label }}
   </h1>
   <p class="text-surface-600 dark:text-surface-400 mb-6 sm:mb-8">
-    {{ digest.startDate | dateDisplay }} &ndash; {{ digest.endDate | dateDisplay }}
+    <time datetime="{{ digest.startDate | isoDate }}">{{ digest.startDate | dateDisplay }}</time> &ndash; <time datetime="{{ digest.endDate | isoDate }}">{{ digest.endDate | dateDisplay }}</time>
     <span class="text-sm">({{ digest.posts.length }} post{% if digest.posts.length != 1 %}s{% endif %})</span>
   </p>