fix: increase base font-weight to 500 for Manrope readability

Manrope at weight 400 is thinner than Open Sans was, making small body
text hard to read. Bumping to 500 matches Rivet.dev's usage.

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

frontend/packages/inspector/index.html

@@ -52,6 +52,7 @@
       body {
         color: var(--text);
         font-family: 'Manrope', system-ui, sans-serif;
+        font-weight: 500;
         font-size: 13px;
         line-height: 1.5;
         -webkit-font-smoothing: antialiased;

frontend/packages/website/src/styles/global.css

@@ -36,6 +36,7 @@
   body {
     @apply bg-black text-white antialiased;
     font-family: 'Manrope', system-ui, sans-serif;
+    font-weight: 500;
   }
 
   /* Text selection - matches rivet.dev */