feat: migrate docs to docusaurus v3 hub

src/css/blackroad-os-brand/tokens.css

@@ -0,0 +1,8 @@
+:root {
+  --br-brand-ink: #0f172a;
+  --br-brand-surface: #0b1020;
+  --br-brand-accent: #6b21a8;
+  --br-brand-glow: #22d3ee;
+  --br-brand-foreground: #e5e7eb;
+  --br-brand-muted: #9ca3af;
+}