Update README and enhance UpdateDialog accessibility

- Updated the README to use a higher resolution icon for better visibility.
- Improved the UpdateDialog component by adding a backdrop button for dismissing the dialog and enhancing accessibility with ARIA attributes.

README.md

@@ -1,5 +1,5 @@
 <p align="center">
-  <img src="resources/icons/png/128x128.png" alt="Claude Code Context" width="120" />
+  <img src="resources/icons/png/512x512.png" alt="Claude Code Context" width="120" />
 </p>
 
 <h1 align="center">Claude Code Context</h1>

src/renderer/components/common/UpdateDialog.tsx

@@ -17,18 +17,24 @@ export const UpdateDialog = (): React.JSX.Element | null => {
   if (!showUpdateDialog) return null;
 
   return (
-    <div
-      className="fixed inset-0 z-50 flex items-center justify-center"
-      style={{ backgroundColor: 'rgba(0, 0, 0, 0.6)' }}
-      onClick={dismissUpdateDialog}
-    >
+    <div className="fixed inset-0 z-50 flex items-center justify-center">
+      {/* Backdrop */}
+      <button
+        className="absolute inset-0 cursor-default"
+        style={{ backgroundColor: 'rgba(0, 0, 0, 0.6)' }}
+        onClick={dismissUpdateDialog}
+        aria-label="Close dialog"
+        tabIndex={-1}
+      />
       <div
         className="relative mx-4 w-full max-w-md rounded-lg border p-6 shadow-xl"
+        role="dialog"
+        aria-modal="true"
+        aria-label="Update available"
         style={{
           backgroundColor: 'var(--color-surface-overlay)',
           borderColor: 'var(--color-border-emphasis)',
         }}
-        onClick={(e) => e.stopPropagation()}
       >
         {/* Close button */}
         <button

src/renderer/components/settings/sections/AdvancedSection.tsx

@@ -72,7 +72,9 @@ export const AdvancedSection = ({
         return (
           <>
             <Download className="size-3.5" />
-            {updateStatus === 'downloaded' ? 'Update ready' : `v${availableVersion} available`}
+            {updateStatus === 'downloaded'
+              ? 'Update ready'
+              : `v${availableVersion ?? 'unknown'} available`}
           </>
         );
       default: