feat: dual theme support for docsite

- Theme toggle in navbar (sun/moon icon)
- Respects system preference (prefers-color-scheme)
- Dark: pure black #000000, white/grey text, no green tint
- Light: white #ffffff, dark grey text, subtle grey borders
- All custom components (theorem-card, green-card, formula,
  metric-card, badges) styled for both themes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: gHashTag

docsite/docusaurus.config.ts

@@ -47,8 +47,8 @@ const config: Config = {
     image: 'img/trinity-social-card.png',
     colorMode: {
       defaultMode: 'dark',
-      disableSwitch: true,
-      respectPrefersColorScheme: false,
+      disableSwitch: false,
+      respectPrefersColorScheme: true,
     },
     navbar: {
       title: 'Trinity',