fix: handle null/invalid nodes_used in metadata generation

Fixed TypeError when generating metadata for templates with missing or
invalid nodes_used data. Added safe JSON parsing with fallback to empty
array.

Root cause: Template -1000 (Canonical AI Tool Examples) has null
nodes_used field, causing iteration error in summarizeNodes().

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

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

src/scripts/fetch-templates.ts

@@ -418,11 +418,27 @@ async function generateTemplateMetadata(db: any, service: TemplateService) {
         console.warn(`Failed to parse workflow for template ${t.id}:`, error);
       }
 
+      // Parse nodes_used safely
+      let nodes: string[] = [];
+      try {
+        if (t.nodes_used) {
+          nodes = JSON.parse(t.nodes_used);
+          // Ensure it's an array
+          if (!Array.isArray(nodes)) {
+            console.warn(`Template ${t.id} has invalid nodes_used (not an array), using empty array`);
+            nodes = [];
+          }
+        }
+      } catch (error) {
+        console.warn(`Failed to parse nodes_used for template ${t.id}:`, error);
+        nodes = [];
+      }
+
       return {
         templateId: t.id,
         name: t.name,
         description: t.description,
-        nodes: JSON.parse(t.nodes_used),
+        nodes: nodes,
         workflow
       };
     });