Set confidence threshold to 80% and remove slider from frontend

✅ Frontend Changes:
- Removed confidence threshold slider from web interface
- Added fixed 80% confidence display with green info box
- Updated JavaScript to use fixed 0.8 threshold
- Removed slider-related CSS styles

✅ Backend Changes:
- Updated all API endpoints to default to 80% confidence (0.8)
- Modified POST /detect, GET /detect/hardcoded, POST /detect/base64
- Updated comments to reflect new default threshold

✅ Testing Updates:
- Updated test_api.py to use 80% confidence for all tests
- Ensures consistent testing with new threshold

✅ Benefits:
- High precision mode (80% confidence) reduces false positives
- Simplified user interface without threshold adjustment
- Consistent detection behavior across all endpoints

test_api.py

@@ -53,7 +53,7 @@ def test_hardcoded_detection():
     """Test detection with hardcoded image."""
     print("\n🖼️  Testing Hardcoded Image Detection...")
     try:
-        response = requests.get(f"{BASE_URL}/detect/hardcoded?confidence=0.5")
+        response = requests.get(f"{BASE_URL}/detect/hardcoded?confidence=0.8")
         if response.status_code == 200:
             data = response.json()
             if data['success']:
@@ -105,7 +105,7 @@ def test_file_upload():
     try:
         with open(test_image_path, 'rb') as f:
             files = {'image': f}
-            data = {'confidence': '0.5'}
+            data = {'confidence': '0.8'}
             response = requests.post(f"{BASE_URL}/detect", files=files, data=data)
         
         if response.status_code == 200:
@@ -165,7 +165,7 @@ def test_base64_detection():
         # Send request
         payload = {
             'image': base64_string,
-            'confidence': 0.5
+            'confidence': 0.8
         }
         
         response = requests.post(