feat: capture Windows temps réel via mini serveur HTTP (port 5006)

- CaptureServer : serveur HTTP daemon sur l'agent Windows
- Capture fraîche mss en ~94ms à chaque requête
- Plus de lecture de vieux heartbeats sur disque
- Fallback capture locale si agent indisponible
- Firewall Windows port 5006 configuré

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

visual_workflow_builder/frontend_v4/src/components/CapturePanel.tsx

@@ -111,25 +111,28 @@ export default function CapturePanel({
     }
   };
 
-  // Capture intelligente — auto-détection OS
+  // Capture intelligente — tente d'abord l'agent Windows distant,
+  // puis fallback sur la capture locale si l'agent est injoignable.
   const doSmartCapture = async () => {
-    const isWindows = navigator.platform?.includes('Win') || navigator.userAgent?.includes('Windows');
-    if (isWindows) {
-      try {
-        const resp = await fetch('/api/screen-capture/capture-windows', { method: 'POST' });
-        const data = await resp.json();
-        if (data.image) {
-          setCurrentCapture({
-            screenshot_base64: data.image,
-            width: data.width,
-            height: data.height,
-            source: 'windows',
-          } as any);
-        }
-      } catch {}
-    } else {
-      onCapture();
+    try {
+      const resp = await fetch('/api/screen-capture/capture-windows', { method: 'POST' });
+      const data = await resp.json();
+      if (resp.ok && data.image) {
+        setCurrentCapture({
+          screenshot_base64: data.image,
+          width: data.width,
+          height: data.height,
+          source: data.source || 'windows',
+        } as any);
+        return;
+      }
+      // Agent indisponible — fallback capture locale
+      console.warn('Agent Windows indisponible, fallback local:', data.error);
+    } catch (err) {
+      console.warn('Erreur capture Windows, fallback local:', err);
     }
+    // Fallback : capture locale (ecran du serveur Linux)
+    onCapture();
   };
 
   const handleTimerCapture = () => {