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

_includes/components/cv-builder.njk

@@ -161,7 +161,7 @@
 {# Last Updated #}
 {% if cv.lastUpdated %}
 <p class="text-sm text-surface-500 text-center mt-8">
-  Last updated: {{ cv.lastUpdated | date("PPP") }}
+  Last updated: <time datetime="{{ cv.lastUpdated }}">{{ cv.lastUpdated | date("PPP") }}</time>
 </p>
 {% endif %}