feat: SaaS closed beta waitlist section

Gauges B2B interest in a commercial tier built on top of Greywall's
open-source core. The plugin SDK angle leans into what people have
actually been asking for: extending Greyproxy with custom heuristics,
Model Council, and token-saving MITM plugins. Web3forms handles signup.

Core stays free and open source; the new tier rides on top.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

components/nav.tsx

@@ -61,6 +61,13 @@ export function Nav() {
             </svg>
             <span className="hidden sm:inline">GitHub</span>
           </a>
+          <a
+            href="#waitlist"
+            className="inline-flex items-center gap-1.5 px-3 py-1.5 rounded-md bg-primary text-primary-foreground text-xs sm:text-sm font-sans font-medium hover:bg-primary/90 transition-colors whitespace-nowrap"
+          >
+            <span className="hidden sm:inline">Join the SaaS beta</span>
+            <span className="sm:hidden">SaaS beta</span>
+          </a>
         </div>
       </div>
     </nav>