website: add diagram Prism language, CodeBlock showLineNumbers prop, brighter dark mode links

- Custom 'diagram' Prism language: box-drawing chars get neutral color,
  text labels get a saturated blue so they pop against the structure
- CodeBlock gains showLineNumbers prop (default true) and skips Prism
  highlighting when lang is empty
- Diagram block in index page uses lang='diagram' with line numbers off
- Dark mode --link-accent bumped from #58a6ff to #79bbff for better
  visibility against dark backgrounds

website/src/styles/editorial-prism.css

@@ -130,6 +130,20 @@ pre[class*='language-'] {
   color: #2563eb;
 }
 
+/* Diagram language: neutral box-drawing, colored text labels */
+.language-diagram .token.box-drawing {
+  color: #c0c0c0;
+}
+
+.language-diagram .token.line-char {
+  color: #c0c0c0;
+}
+
+.language-diagram .token.label {
+  color: #0550ae;
+  font-weight: 600;
+}
+
 /* No text shadow on any token */
 .token {
   text-shadow: none;
@@ -159,6 +173,8 @@ pre[class*='language-'] {
     --prism-spread: #ff7b72;
     --prism-regex: #a5d6ff;
     --prism-bash-fn: #79c0ff;
+    --prism-diagram-structure: #555;
+    --prism-diagram-label: #79bbff;
   }
 }
 
@@ -284,3 +300,16 @@ pre[class*='language-'] {
     color: var(--prism-bash-fn);
   }
 }
+
+.language-diagram .token.box-drawing,
+.language-diagram .token.line-char {
+  @variant dark {
+    color: var(--prism-diagram-structure);
+  }
+}
+
+.language-diagram .token.label {
+  @variant dark {
+    color: var(--prism-diagram-label);
+  }
+}

website/src/styles/globals.css

@@ -174,7 +174,7 @@
       rgba(255, 255, 255, 0.05) 0px 2px 8px, rgba(255, 255, 255, 0.02) 0px 4px 16px,
       rgba(255, 255, 255, 0.06) 0px 0px 0px 1px inset;
 
-    --link-accent: #58a6ff;
+    --link-accent: #79bbff;
     --brand-primary: #60a5fa;
     --brand-secondary: #f5a623;