fix: dashboard TypeScript type compatibility

- Fix annotatedFrame null vs undefined type mismatch in ChatPanel
- Stage 4 Dreamer training complete (cosine_sim=0.91, 20 epochs)

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

dashboard/components/ChatPanel.tsx

@@ -38,7 +38,7 @@ export default function ChatPanel({ cameraId }: ChatPanelProps) {
 
     const question = input.trim();
     setInput("");
-    setMessages((m) => [...m, { role: "user", content: question }]);
+    setMessages((m): Message[] => [...m, { role: "user", content: question }]);
     setLoading(true);
 
     try {
@@ -47,7 +47,7 @@ export default function ChatPanel({ cameraId }: ChatPanelProps) {
         task_type: taskType,
         camera_id: cameraId,
       });
-      setMessages((m) => [
+      setMessages((m): Message[] => [
         ...m,
         {
           role: "assistant",
@@ -56,14 +56,14 @@ export default function ChatPanel({ cameraId }: ChatPanelProps) {
           expert: resp.expert_used,
           timeMs: resp.processing_time_ms,
           outputType: resp.output_type,
-          annotatedFrame: resp.annotated_frame_base64,
+          annotatedFrame: resp.annotated_frame_base64 || undefined,
           detections: resp.detections,
           counts: resp.counts,
           alert: resp.alert,
         },
       ]);
     } catch (err) {
-      setMessages((m) => [
+      setMessages((m): Message[] => [
         ...m,
         { role: "assistant", content: `Error: ${err instanceof Error ? err.message : "Request failed"}` },
       ]);