webui: Add Mermaid diagram support to markdown

* Installed mermaid library
* Extended markdown renderer to support mermaid code blocks
* Added CSS styling for mermaid diagrams
* Added a demo page for testing mermaid diagrams

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/webui/src/web-components/demo/mermaid-test/index.html b/webui/src/web-components/demo/mermaid-test/index.html
new file mode 100644
index 0000000..e2fd202
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+++ b/webui/src/web-components/demo/mermaid-test/index.html
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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>Mermaid Diagram Test</title>
+  <script type="module" src="./mermaid-test.ts"></script>
+  <style>
+    body {
+      font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
+      padding: 20px;
+      max-width: 1000px;
+      margin: 0 auto;
+    }
+    h1 {
+      color: #333;
+    }
+    .container {
+      border: 1px solid #ddd;
+      border-radius: 4px;
+      padding: 20px;
+      margin: 20px 0;
+    }
+  </style>
+</head>
+<body>
+  <h1>Mermaid Diagram Testing</h1>
+  <p>This page tests the integration of Mermaid diagrams in the markdown renderer.</p>
+  
+  <div class="container">
+    <mermaid-test-component></mermaid-test-component>
+  </div>
+</body>
+</html>
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