fix(scanner): yield to scheduler before runSync + min skeleton + gallery placeholder

- useDetection.analyze() now awaits a requestAnimationFrame before
  calling runInference. Without it React commits isAnalyzing=true and
  immediately hits the synchronous TFLite runSync that blocks the JS
  thread for 500-1500ms — the analyzing skeleton overlay appears AFTER
  the inference, defeating its purpose.
- Same hook enforces a minimum 600ms total before resolving so a
  cached/fast inference doesn't show a skeleton flicker that reads as
  a glitch.
- ScannerScreen.handleCapture is split: capture stays inline,
  processImage(uri) is now its own async function. Cleaner control
  flow when a take succeeds but analysis is delegated.
- The previously dead "image gallery" icon next to the shutter is now
  a real TouchableOpacity that fires a "coming soon" toast (we'll wire
  it to expo-image-picker once we add the lib + native rebuild).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

VinEye/src/hooks/useDetection.ts

@@ -11,8 +11,21 @@ export function useDetection() {
     setIsAnalyzing(true);
     setError(null);
 
+    // Yield au scheduler pour que React commit le render `isAnalyzing=true`
+    // (le skeleton overlay) AVANT que runSync() ne bloque le JS thread ~500-1500ms.
+    await new Promise<void>((resolve) =>
+      requestAnimationFrame(() => resolve()),
+    );
+
+    const startedAt = Date.now();
     try {
       const detection = await runInference(imageUri);
+      // UX : maintenir le skeleton visible au moins 600ms pour éviter un flash
+      // perçu comme un bug ("rien ne se passe") quand l'inférence est très rapide.
+      const elapsed = Date.now() - startedAt;
+      if (elapsed < 600) {
+        await new Promise((r) => setTimeout(r, 600 - elapsed));
+      }
       setLastDetection(detection);
       return detection;
     } catch (err) {

VinEye/src/screens/ScannerScreen.tsx

@@ -93,49 +93,11 @@ export default function ScannerScreen() {
     };
   }, []);
 
-  async function handleCapture() {
-    if (isAnalyzing) return;
-
-    if (!cameraRef.current) {
-      Alert.alert(t('common.error'), 'Camera not initialized');
-      return;
-    }
-    if (!isCameraReady) {
-      Alert.alert(t('common.error'), 'Camera is not ready yet — please wait.');
-      return;
-    }
-
-    await hapticLight();
-
-    shutterScale.value = withSequence(
-      withTiming(0.88, { duration: 100 }),
-      withTiming(1, { duration: 150 })
-    );
-
+  async function processImage(imageUri: string) {
     const interval = setInterval(() => {
       setLiveConfidence((prev) => Math.min(prev + Math.floor(Math.random() * 12), 85));
     }, 150);
 
-    let imageUri: string | undefined;
-    try {
-      const photo = await cameraRef.current.takePictureAsync({
-        quality: 0.85,
-        skipProcessing: true,
-        exif: false,
-      });
-      imageUri = photo?.uri;
-      if (__DEV__) {
-        console.log('[Scanner] Captured photo:', imageUri);
-      }
-    } catch (err) {
-      clearInterval(interval);
-      setLiveConfidence(0);
-      const message = err instanceof Error ? err.message : String(err);
-      console.warn('[Scanner] takePictureAsync failed:', message);
-      Alert.alert(t('common.error'), `Capture failed: ${message}`);
-      return;
-    }
-
     const [detection, coords] = await Promise.all([
       analyze(imageUri),
       requestAndGetLocation(),
@@ -172,6 +134,61 @@ export default function ScannerScreen() {
     setTimeout(() => setLiveConfidence(0), 500);
   }
 
+  async function handleCapture() {
+    if (isAnalyzing) return;
+
+    if (!cameraRef.current) {
+      Alert.alert(t('common.error'), 'Camera not initialized');
+      return;
+    }
+    if (!isCameraReady) {
+      Alert.alert(t('common.error'), 'Camera is not ready yet — please wait.');
+      return;
+    }
+
+    await hapticLight();
+
+    shutterScale.value = withSequence(
+      withTiming(0.88, { duration: 100 }),
+      withTiming(1, { duration: 150 })
+    );
+
+    let imageUri: string | undefined;
+    try {
+      const photo = await cameraRef.current.takePictureAsync({
+        quality: 0.85,
+        skipProcessing: true,
+        exif: false,
+      });
+      imageUri = photo?.uri;
+      if (__DEV__) {
+        console.log('[Scanner] Captured photo:', imageUri);
+      }
+    } catch (err) {
+      setLiveConfidence(0);
+      const message = err instanceof Error ? err.message : String(err);
+      console.warn('[Scanner] takePictureAsync failed:', message);
+      Alert.alert(t('common.error'), `Capture failed: ${message}`);
+      return;
+    }
+
+    if (!imageUri) {
+      setLiveConfidence(0);
+      return;
+    }
+
+    await processImage(imageUri);
+  }
+
+  async function handlePickFromGallery() {
+    // TODO: réactiver après rebuild natif Android (expo prebuild + run:android)
+    // pour ajouter `expo-image-picker` au build natif
+    await hapticLight();
+    toast.info(t('scanner.galleryComingSoonTitle'), {
+      description: t('scanner.galleryComingSoonDescription'),
+    });
+  }
+
   if (!permission) {
     return (
       <View className="flex-1 items-center justify-center bg-[#FAFAFA]">
@@ -252,12 +269,21 @@ export default function ScannerScreen() {
         )}
 
         <View className="absolute bottom-0 left-0 right-0 flex-row items-center justify-between px-8 pb-12 pt-5">
-          <View
+          <TouchableOpacity
             className="h-11 w-11 items-center justify-center rounded-lg"
-            style={{ backgroundColor: 'rgba(255,255,255,0.15)', borderWidth: 1, borderColor: 'rgba(255,255,255,0.3)' }}
+            style={{
+              backgroundColor: 'rgba(255,255,255,0.15)',
+              borderWidth: 1,
+              borderColor: 'rgba(255,255,255,0.3)',
+              opacity: isAnalyzing ? 0.4 : 1,
+            }}
+            onPress={handlePickFromGallery}
+            disabled={isAnalyzing}
+            accessibilityLabel={t('scanner.pickFromGallery')}
+            activeOpacity={0.7}
           >
-            <Ionicons name="image-outline" size={20} color="rgba(255,255,255,0.5)" />
-          </View>
+            <Ionicons name="image-outline" size={20} color={colors.surface} />
+          </TouchableOpacity>
 
           <Animated.View
             className="h-[72px] w-[72px] items-center justify-center rounded-full border-[3px] border-white"