feat: Inter font, weight 450, bumped base sizes across all pages

- Load Inter variable font from Google Fonts on all 5 HTML pages
- font-weight: 450 on body (between regular and medium — fixes thin feel)
- -webkit-font-smoothing: antialiased for cleaner screen rendering
- Base font size: normal 16→17px, large 18→19px, small 14→15px
- Applies consistently to main UI, login, setup, settings, and help pages

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

cortex/static/setup.html

@@ -4,6 +4,9 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>Cortex — Setup</title>
+  <link rel="preconnect" href="https://fonts.googleapis.com">
+  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
+  <link href="https://fonts.googleapis.com/css2?family=Inter:wght@100..900&display=swap" rel="stylesheet">
   <style>
     *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
 
@@ -13,7 +16,10 @@
       align-items: center;
       justify-content: center;
       background: #0f1117;
-      font-family: system-ui, -apple-system, sans-serif;
+      font-family: 'Inter', system-ui, -apple-system, sans-serif;
+      font-weight: 450;
+      -webkit-font-smoothing: antialiased;
+      -moz-osx-font-smoothing: grayscale;
       color: #e2e8f0;
       padding: 1.5rem;
     }