fix: Improve Mermaid code block detection and fix duplicate variable

- Fixed duplicate svg variable declaration
- Improved code block detection with multiple selectors
- Added fallback to detect mermaid syntax in all code blocks
- Better handling of Jekyll/Kramdown rendered code blocks

Author: rayraycodes

docs_site/_layouts/default.html

@@ -674,9 +674,9 @@
         mermaidEl.style.height = 'auto';
       }
 
-      const svg = wrapper.querySelector('svg');
-      if (svg) {
-        svg.style.cssText = 'display: block !important; visibility: visible !important; opacity: 1 !important; width: auto !important; height: auto !important; max-width: none !important; max-height: none !important;';
+      const svgEl = wrapper.querySelector('svg');
+      if (svgEl) {
+        svgEl.style.cssText = 'display: block !important; visibility: visible !important; opacity: 1 !important; width: auto !important; height: auto !important; max-width: none !important; max-height: none !important;';
       }
 
       // Center scroll position after a brief moment