fix: remove backdrop-blur overlay causing blurry text site-wide

The full-screen glassmorphism overlay had backdrop-blur-[0.5px] which
triggered GPU compositing on the entire viewport, degrading subpixel
text rendering inconsistently. Also use globalThis.fetch (not SvelteKit
fetch) when forwarding session token in admin SSR calls to avoid header
stripping.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/+layout.svelte

@@ -58,7 +58,7 @@
 
     <!-- Glassmorphism overlay -->
     <div
-      class="absolute inset-0 bg-gradient-to-br from-primary/2 via-transparent to-accent/2 backdrop-blur-[0.5px]"
+      class="absolute inset-0 bg-gradient-to-br from-primary/2 via-transparent to-accent/2"
     ></div>
   </div>
   <!-- Header -->