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/style.css

@@ -94,7 +94,10 @@
         }
 
         body {
-            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;
             background: var(--bg);
             color: var(--text);
             height: 100vh;