Soften modal background with radial gradient

- Replace solid black 50% opacity with radial gradient
- Center: 80% black (rgba(0,0,0,0.8))
- Corners: 70% black (rgba(0,0,0,0.7))
- Apply to both ModelSelectionModal and McpServerModal
- Creates softer, more visually appealing backdrop
- Remove bg-black bg-opacity-50 classes and use inline style

examples/chat-ui/src/components/McpServerModal.tsx

@@ -240,7 +240,8 @@ const McpServerModal: React.FC<McpServerModalProps> = ({
   return (
     <>
       <div 
-        className={`fixed inset-0 bg-black bg-opacity-50 z-50 flex items-center justify-center p-4 ${isOpen ? 'block' : 'hidden'}`}
+        className={`fixed inset-0 z-50 flex items-center justify-center p-4 ${isOpen ? 'block' : 'hidden'}`}
+        style={{ background: 'radial-gradient(circle, rgba(0,0,0,0.8) 0%, rgba(0,0,0,0.7) 100%)' }}
         onClick={onClose}
       >
         <div 

examples/chat-ui/src/components/ModelSelectionModal.tsx

@@ -87,7 +87,8 @@ const ModelSelectionModal: React.FC<ModelSelectionModalProps> = ({
   return (
     <>
       <div 
-        className="fixed inset-0 bg-black bg-opacity-50 z-50 flex items-center justify-center p-4"
+        className="fixed inset-0 z-50 flex items-center justify-center p-4"
+        style={{ background: 'radial-gradient(circle, rgba(0,0,0,0.8) 0%, rgba(0,0,0,0.7) 100%)' }}
         onClick={onClose}
       >
         <div