fix(ascii): replace Google Fonts CDN with local fonts.css

ASCII generator now renders in bundled JetBrains Mono without internet,
matching the preview pane.

src/ascii-generator.html

@@ -4,10 +4,7 @@
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>ASCII Art Generator - MarkdownConverter</title>
-    <link
-      href="https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;500;600&display=swap"
-      rel="stylesheet"
-    />
+    <link rel="stylesheet" href="../fonts.css" />
     <style>
       :root {
         --ci-dark-gray: #464646;
@@ -140,11 +137,12 @@
       }
 
       .preview-content {
-        font-family: 'JetBrains Mono', monospace;
+        font-family: 'JetBrains Mono', 'Fira Code', monospace;
         font-size: 12px;
         line-height: 1.3;
         color: #00ff00;
         white-space: pre;
+        font-feature-settings: 'liga' 0, 'calt' 0, 'dlig' 0;
       }
 
       .template-grid {