fix(#190,#191): fix XSS vulnerabilities in Mermaid and WikiLink rendering

CRITICAL SECURITY FIXES for two XSS vulnerabilities

Mermaid XSS Fix (#190):
- Changed securityLevel from "loose" to "strict"
- Disabled htmlLabels to prevent HTML injection
- Blocks script execution and event handlers in SVG output

WikiLink XSS Fix (#191):
- Added alphanumeric whitelist validation for slugs
- Escape HTML entities in title attribute
- Reject slugs with special characters that could break attributes
- Return escaped text for invalid slugs

Security Impact:
- Prevents account takeover via cookie theft
- Blocks malicious script execution in user browsers
- Enforces strict content security for user-provided content

Fixes #190, #191

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/components/knowledge/WikiLinkRenderer.tsx

@@ -56,14 +56,20 @@ function parseWikiLinks(html: string): string {
     const trimmedSlug = slug.trim();
     const text = displayText?.trim() ?? trimmedSlug;
 
+    // Validate slug contains only safe characters
+    if (!/^[a-zA-Z0-9\-_./]+$/.test(trimmedSlug)) {
+      // Invalid slug - return original text without creating a link
+      return escapeHtml(match);
+    }
+
     // Create a styled link
     // Using data-wiki-link attribute for styling and click handling
-    return `<a 
+    return `<a
       href="/knowledge/${encodeURIComponent(trimmedSlug)}"
       data-wiki-link="true"
       data-slug="${encodeURIComponent(trimmedSlug)}"
       class="wiki-link text-blue-600 dark:text-blue-400 hover:text-blue-800 dark:hover:text-blue-300 underline decoration-dotted hover:decoration-solid transition-colors"
-      title="Go to ${trimmedSlug}"
+      title="Go to ${escapeHtml(trimmedSlug)}"
     >${escapeHtml(text)}</a>`;
   });
 }

apps/web/src/components/mindmap/MermaidViewer.tsx

@@ -36,10 +36,10 @@ export function MermaidViewer({
         theme: isDark ? "dark" : "default",
         flowchart: {
           useMaxWidth: true,
-          htmlLabels: true,
+          htmlLabels: false,
           curve: "basis",
         },
-        securityLevel: "loose",
+        securityLevel: "strict",
       });
 
       // Generate unique ID for this render