feat(docs): comprehensive GitHub Primer theme overhaul with dark mode fix

- Fix broken dark mode by correcting palette toggle order and setting primary/accent to custom
- Rewrite extra.css with full GitHub Primer color scheme (light: #ffffff/#0969da, dark: #0d1117/#1f6feb)
- Style header, sidebar, buttons, cards, code blocks, and tables to match GitHub aesthetic
- Add Open Graph and Twitter Card meta tags via main.html override
- Add JSON-LD structured data (WebSite + SoftwareApplication schemas)
- Add announcement bar (v2.1.2 release)
- Add custom 404 page with navigation buttons
- Remove inline styles from skills/index.md (moved to extra.css)
- Mobile responsive adjustments for hero sections

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/skills/index.md

@@ -5,57 +5,6 @@ hide:
   - edit
 ---
 
-<style>
-.skills-hero {
-  text-align: center;
-  padding: 2rem 1rem 0.5rem;
-  max-width: 700px;
-  margin: 0 auto;
-}
-
-.skills-hero h1 {
-  font-size: 2.2rem !important;
-  font-weight: 800 !important;
-  letter-spacing: -0.03em;
-  line-height: 1.15;
-  margin-bottom: 0.5rem !important;
-  background: linear-gradient(135deg, #a78bfa 0%, #e879f9 50%, #f59e0b 100%);
-  -webkit-background-clip: text;
-  -webkit-text-fill-color: transparent;
-  background-clip: text;
-}
-
-[data-md-color-scheme="default"] .skills-hero h1 {
-  background: linear-gradient(135deg, #7c3aed 0%, #c026d3 50%, #d97706 100%);
-  -webkit-background-clip: text;
-  -webkit-text-fill-color: transparent;
-  background-clip: text;
-}
-
-.skills-hero-sub {
-  font-size: 1.05rem;
-  opacity: 0.6;
-  max-width: 520px;
-  margin: 0 auto 1.5rem;
-}
-
-.domain-section {
-  margin-top: 1rem;
-}
-
-.skill-count {
-  display: inline-block;
-  background: var(--md-primary-fg-color);
-  color: var(--md-primary-bg-color);
-  font-size: 0.7rem;
-  font-weight: 700;
-  padding: 0.15rem 0.5rem;
-  border-radius: 999px;
-  vertical-align: middle;
-  margin-left: 0.35rem;
-}
-</style>
-
 <div class="skills-hero" markdown>
 
 # Skills Library