fix(docs): visible admonition icons in dark mode (#516 follow-up)

The asciidoctor stylesheet hardcodes dark admonition icon colors (note
#19407c, tip #111, important #bf0000, warning/caution dark warm tones)
that nearly vanish on the dark #1f2937 panel — measured contrast 1.3-2.3:1,
below the 3:1 WCAG threshold for non-text. Add dark-scoped overrides to
light, semantic colours (note blue, tip green, warning amber, caution
orange, important red); contrast now 5-8:1. Light mode unchanged.

Note: Lighthouse reports Accessibility 100 but only audits the default
(light) theme — dark mode is a class toggle it never triggers — so these
dark-mode contrast issues are invisible to it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: raifdmueller

website/src/styles/main.css

@@ -411,6 +411,26 @@ html {
   border-left-color: #374151;
 }
 
+/* The asciidoctor stylesheet hardcodes dark admonition icon colors (note
+   #19407c, tip #111, important #bf0000, …) that nearly vanish on the dark
+   panel (contrast ~1.3-2.3:1, below the 3:1 needed for non-text). Lift each to
+   a light, semantic colour for dark mode. (#516 follow-up) */
+.dark .asciidoc-content .admonitionblock td.icon .icon-note::before {
+  color: #60a5fa;
+}
+.dark .asciidoc-content .admonitionblock td.icon .icon-tip::before {
+  color: #4ade80;
+}
+.dark .asciidoc-content .admonitionblock td.icon .icon-warning::before {
+  color: #fbbf24;
+}
+.dark .asciidoc-content .admonitionblock td.icon .icon-caution::before {
+  color: #fb923c;
+}
+.dark .asciidoc-content .admonitionblock td.icon .icon-important::before {
+  color: #f87171;
+}
+
 .dark .asciidoc-content hr {
   border-color: #374151;
 }