fix: handle undefined npmKeywords in tool detail page

Add null check before accessing npmKeywords.length to prevent
runtime TypeError when npmKeywords is undefined.

Fixes: Cannot read properties of undefined (reading 'length')

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/web/src/app/tool/[...slug]/page.tsx

@@ -446,7 +446,7 @@ export default function ToolDetailPage({
             </Card>
 
             {/* NPM Keywords */}
-            {tool.npmKeywords.length > 0 && (
+            {tool.npmKeywords && tool.npmKeywords.length > 0 && (
               <Card>
                 <CardHeader>
                   <CardTitle>NPM Keywords</CardTitle>