Add light mode support (next-themes), JetBrains Mono font, OpenType features

- layout.tsx: ThemeProvider from next-themes, light mode DEFAULT, JetBrains_Mono font
- globals.css: font-mono pointing to correct variable, font-feature-settings cv01+ss03 on body
- next-themes package installed
- Build passes with zero errors

web/src/app/globals.css

@@ -8,7 +8,7 @@
   --color-background: var(--background);
   --color-foreground: var(--foreground);
   --font-sans: var(--font-sans);
-  --font-mono: var(--font-geist-mono);
+  --font-mono: var(--font-mono);
   --font-heading: var(--font-sans);
   --color-sidebar-ring: var(--sidebar-ring);
   --color-sidebar-border: var(--sidebar-border);
@@ -123,6 +123,7 @@
   }
   body {
     @apply bg-background text-foreground;
+    font-feature-settings: "cv01" 1, "ss03" 1;
   }
   html {
     @apply font-sans;