fix(tunnels): use is:global style for dynamically created elements

Astro scopes non-global styles, so tunnel entry cards and diagrams
created via JS innerHTML had no styling. Same pattern used by the
config page.

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

Author: luizomf

src/pages/tunnels.astro

@@ -161,7 +161,7 @@ import Tooltip from '../components/Tooltip.astro';
   <Footer />
 </Base>
 
-<style>
+<style is:global>
   .page-header {
     text-align: center;
     padding: 2rem 0 1.5rem;