feat: improve camera permission handling for QR scanner

- Add pre-check for camera devices to trigger permission prompt
- Add helpful info message explaining camera permission requirement
- Implement fallback to try default camera if facingMode constraint fails
- Better error messages for different camera access scenarios
- Log errors to console for debugging
- Handle NotAllowedError, NotFoundError, NotReadableError, OverconstrainedError

src/components/event/QRCodeScanner.tsx

@@ -26,6 +26,18 @@ export function QRCodeScanner({ onScan, onError }: QRCodeScannerProps) {
   const startScanning = async () => {
     try {
       setError(null);
+      
+      // First, check if we can get camera devices (this will trigger permission prompt)
+      try {
+        const devices = await Html5Qrcode.getCameras();
+        if (!devices || devices.length === 0) {
+          throw new Error('No camera found on this device.');
+        }
+      } catch (permErr: any) {
+        // If we can't get cameras, it might be a permission issue
+        console.error('Camera access error:', permErr);
+      }
+
       const scanner = new Html5Qrcode(scannerIdRef.current);
       scannerRef.current = scanner;
 
@@ -60,16 +72,23 @@ export function QRCodeScanner({ onScan, onError }: QRCodeScannerProps) {
     } catch (err: any) {
       let errorMsg = 'Failed to start camera';
       
-      if (err.message?.includes('Permission')) {
-        errorMsg = 'Camera permission denied. Please allow camera access in your browser settings.';
-      } else if (err.message?.includes('NotFoundError')) {
+      console.error('Scanner error:', err);
+      
+      if (err.name === 'NotAllowedError' || err.message?.includes('NotAllowedError')) {
+        errorMsg = 'Camera permission denied. Please click "Allow" when your browser asks for camera access.';
+      } else if (err.name === 'NotFoundError' || err.message?.includes('NotFoundError')) {
         errorMsg = 'No camera found on this device.';
-      } else if (err.message?.includes('NotAllowedError')) {
-        errorMsg = 'Camera access was denied. Please grant permission and try again.';
-      } else if (err.message?.includes('NotReadableError')) {
+      } else if (err.name === 'NotReadableError' || err.message?.includes('NotReadableError')) {
         errorMsg = 'Camera is already in use by another application.';
-      } else if (err.message?.includes('secure')) {
+      } else if (err.name === 'OverconstrainedError' || err.message?.includes('OverconstrainedError')) {
+        errorMsg = 'Camera constraints not supported. Trying with default camera...';
+        // Try again without facingMode constraint
+        setTimeout(() => startScanningWithoutConstraints(), 1000);
+        return;
+      } else if (err.message?.includes('secure') || err.message?.includes('https')) {
         errorMsg = 'Camera access requires HTTPS. Use manual input instead.';
+      } else if (err.message) {
+        errorMsg = `Camera error: ${err.message}`;
       }
       
       setError(errorMsg);
@@ -79,6 +98,50 @@ export function QRCodeScanner({ onScan, onError }: QRCodeScannerProps) {
     }
   };
 
+  const startScanningWithoutConstraints = async () => {
+    try {
+      setError(null);
+      const scanner = new Html5Qrcode(scannerIdRef.current);
+      scannerRef.current = scanner;
+
+      // Try with any available camera
+      const devices = await Html5Qrcode.getCameras();
+      if (devices && devices.length > 0 && devices[0]) {
+        await scanner.start(
+          devices[0].id, // Use first available camera
+          {
+            fps: 10,
+            qrbox: { width: 250, height: 250 },
+          },
+          (decodedText) => {
+            try {
+              const data = JSON.parse(decodedText);
+              if (data.type === 'attendee-checkin' && data.userId) {
+                onScan(data.userId);
+              } else {
+                const errorMsg = 'Invalid QR code format';
+                setError(errorMsg);
+                onError?.(errorMsg);
+              }
+            } catch (err) {
+              const errorMsg = 'Failed to parse QR code';
+              setError(errorMsg);
+              onError?.(errorMsg);
+            }
+          },
+          () => {
+            // Ignore scanning errors
+          }
+        );
+        setIsScanning(true);
+      }
+    } catch (err: any) {
+      console.error('Fallback scanner error:', err);
+      setError('Unable to access camera. Please use manual check-in instead.');
+      setShowManualInput(true);
+    }
+  };
+
   const stopScanning = async () => {
     if (scannerRef.current) {
       try {
@@ -111,6 +174,21 @@ export function QRCodeScanner({ onScan, onError }: QRCodeScannerProps) {
 
   return (
     <div className="space-y-4">
+      {/* Info message before scanning */}
+      {!isScanning && !error && (
+        <div className="bg-blue-50 border border-blue-200 text-blue-800 px-4 py-3 rounded-lg">
+          <div className="flex items-start">
+            <svg className="w-5 h-5 mr-2 mt-0.5 flex-shrink-0" fill="currentColor" viewBox="0 0 20 20">
+              <path fillRule="evenodd" d="M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7-4a1 1 0 11-2 0 1 1 0 012 0zM9 9a1 1 0 000 2v3a1 1 0 001 1h1a1 1 0 100-2v-3a1 1 0 00-1-1H9z" clipRule="evenodd" />
+            </svg>
+            <div className="text-sm">
+              <p className="font-medium mb-1">Camera Permission Required</p>
+              <p>When you click "Start Camera Scan", your browser will ask for camera permission. Please click "Allow" to enable QR code scanning.</p>
+            </div>
+          </div>
+        </div>
+      )}
+
       <div
         id={scannerIdRef.current}
         className="w-full rounded-lg overflow-hidden bg-black"