Add premium subscription CTA to header

Added a prominent call-to-action in the header promoting AI Adopters Club premium subscription with instant access to enterprise resources.

Features:
- Highlighted box with accent border and background tint
- Clear value proposition: enterprise case studies, workflows, prompts, AI chatbot
- Prominent "Unlock Premium Access" button with red accent styling
- Links to aiadopters.club/subscribe
- Responsive layout: side-by-side on desktop, stacked on mobile
- External link icon for clarity

Design:
- bg-accent/10 background with 2px accent border
- Rounded corners for modern look
- Positioned after bio, before social links
- Button uses full accent color for maximum visibility
- Hover state for better interactivity

Value proposition highlights:
✓ Growing library of enterprise case studies
✓ Premium workflows and business prompts
✓ Custom AI chatbot trained on premium assets
✓ Instant access upon subscription

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

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

src/components/Header.tsx

@@ -32,6 +32,26 @@ const Header = () => {
               This library contains citation-ready claims from my research and consulting work. Each claim is backed by data, includes context, and is optimized for LLM extraction.
             </p>
 
+            {/* Premium CTA */}
+            <div className="bg-accent/10 border-2 border-accent rounded-lg p-6 mt-6">
+              <div className="flex flex-col md:flex-row md:items-center gap-4">
+                <div className="flex-1">
+                  <p className="text-sm font-medium text-foreground mb-1">
+                    Get instant access to a growing library of enterprise case studies, premium workflows, business prompts, and our custom AI chatbot trained on all premium assets.
+                  </p>
+                </div>
+                <a
+                  href="https://aiadopters.club/subscribe"
+                  target="_blank"
+                  rel="noopener noreferrer"
+                  className="bg-accent hover:bg-accent/90 text-accent-foreground font-semibold px-6 py-3 rounded-lg transition-colors whitespace-nowrap text-center inline-flex items-center justify-center gap-2"
+                >
+                  Unlock Premium Access
+                  <ExternalLink className="h-4 w-4" />
+                </a>
+              </div>
+            </div>
+
             <div className="flex flex-wrap gap-4 pt-2">
               <a
                 href="https://www.linkedin.com/in/kbanc/"