refactor: update button colors in CallToAction and Hero components for improved contrast

- Changed link button color from cyan to white in agents, home, and network CallToAction components
- Updated network Hero secondary button from dark to gray outline variant

src/pages/agents/CallToAction.tsx

@@ -69,7 +69,7 @@ export function CallToAction() {
                 as="a"
                 to="https://threefold.info/mycelium_network/docs/"
                 variant="link"
-                color="cyan"
+                color="white"
                 className="inline-flex items-center gap-1.5"
                 target="_blank"
                 rel="noopener noreferrer"