feat: send missing node data to ClickHouse for observability

When users open/import a workflow with missing nodes, the frontend
already tracks this via Mixpanel. This adds a parallel fire-and-forget
POST to /api/internal/cloud_analytics so the data also lands in
ClickHouse as "frontend:missing_nodes_detected" events.

This enables post-hoc analysis of which unsupported custom nodes
users are trying to use, supporting data-driven prioritization
of new node pack additions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/platform/telemetry/providers/cloud/MixpanelTelemetryProvider.ts

@@ -8,6 +8,7 @@ import {
   clearTopupTracking as clearTopupUtil,
   startTopupTracking as startTopupUtil
 } from '@/platform/telemetry/topupTracker'
+import { api } from '@/scripts/api'
 import type { AuditLog } from '@/services/customerEventsService'
 
 import { getExecutionContext } from '../../utils/getExecutionContext'
@@ -359,10 +360,39 @@ export class MixpanelTelemetryProvider implements TelemetryProvider {
 
   trackWorkflowImported(metadata: WorkflowImportMetadata): void {
     this.trackEvent(TelemetryEvents.WORKFLOW_IMPORTED, metadata)
+    this.reportMissingNodesToClickHouse(metadata)
   }
 
   trackWorkflowOpened(metadata: WorkflowImportMetadata): void {
     this.trackEvent(TelemetryEvents.WORKFLOW_OPENED, metadata)
+    this.reportMissingNodesToClickHouse(metadata)
+  }
+
+  /**
+   * Send missing node data to ClickHouse via the backend cloud_analytics endpoint.
+   * This supplements the Mixpanel tracking with data in our own analytics pipeline,
+   * enabling post-hoc analysis of which unsupported nodes users are trying to use.
+   * Fire-and-forget — errors are silently ignored.
+   */
+  private reportMissingNodesToClickHouse(
+    metadata: WorkflowImportMetadata
+  ): void {
+    if (metadata.missing_node_count <= 0) return
+
+    api
+      .fetchApi('/internal/cloud_analytics', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          event_name: 'missing_nodes_detected',
+          event_data: {
+            missing_class_types: metadata.missing_node_types,
+            missing_count: metadata.missing_node_count,
+            source: metadata.open_source ?? 'unknown'
+          }
+        })
+      })
+      .catch(() => {})
   }
 
   trackWorkflowSaved(metadata: WorkflowSavedMetadata): void {