style: adopt unified brand CSS system

- Update tokens.css with full brand color palette (neon spectrum, neutrals, surfaces)
- Update custom.css to use brand variables for Docusaurus theming
- Escape MDX template placeholders in RFC template
- Temporarily set onBrokenLinks to warn for build

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

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

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

@@ -1,8 +1,52 @@
+/* BlackRoad OS Brand Tokens - synced with brand.blackroad.io */
 :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;
+  /* Neon Spectrum */
+  --br-sunrise: #FF9D00;
+  --br-warm-orange: #FF6B00;
+  --br-hot-pink: #FF0066;
+  --br-electric-magenta: #FF006B;
+  --br-deep-magenta: #D600AA;
+  --br-vivid-purple: #7700FF;
+  --br-cyber-blue: #0066FF;
+
+  /* Neutrals (darker - almost black) */
+  --br-black: #000000;
+  --br-deep-black: #050505;
+  --br-charcoal: #0D0D0D;
+  --br-slate: #141414;
+  --br-white: #FFFFFF;
+
+  /* Gradients */
+  --br-gradient-brand: linear-gradient(180deg, #FF9D00 0%, #FF6B00 50%, #FF0066 100%);
+  --br-gradient-os: linear-gradient(180deg, #FF0066 0%, #D600AA 33%, #7700FF 66%, #0066FF 100%);
+
+  /* Semantic Colors */
+  --br-action: var(--br-sunrise);
+  --br-creativity: var(--br-hot-pink);
+  --br-intelligence: var(--br-vivid-purple);
+  --br-trust: var(--br-cyber-blue);
+  --br-focus: var(--br-electric-magenta);
+  --br-depth: var(--br-deep-magenta);
+
+  /* Surfaces */
+  --br-surface-base: var(--br-black);
+  --br-surface-elevated: var(--br-deep-black);
+  --br-surface-card: var(--br-charcoal);
+  --br-text-primary: var(--br-white);
+  --br-text-secondary: rgba(255, 255, 255, 0.7);
+  --br-text-muted: rgba(255, 255, 255, 0.5);
+
+  /* Glow Shadows */
+  --br-glow-orange: 0 0 30px rgba(255, 157, 0, 0.4);
+  --br-glow-pink: 0 0 30px rgba(255, 0, 102, 0.4);
+  --br-glow-purple: 0 0 30px rgba(119, 0, 255, 0.4);
+  --br-glow-blue: 0 0 30px rgba(0, 102, 255, 0.4);
+
+  /* Legacy mappings for existing code */
+  --br-brand-ink: var(--br-black);
+  --br-brand-surface: var(--br-surface-base);
+  --br-brand-accent: var(--br-vivid-purple);
+  --br-brand-glow: var(--br-cyber-blue);
+  --br-brand-foreground: var(--br-text-primary);
+  --br-brand-muted: var(--br-text-secondary);
 }