control-plane: Fix save button alignment in filename header

Add w-full to the header's inner flex container so justify-between
pushes the save button to the right end.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: limeburst

control-plane/src/components/browser/FileExplorer.tsx

@@ -346,7 +346,7 @@ export default function FileExplorer({ initialFiles, userLoginName }: FileExplor
       <div className="flex-1 flex flex-col min-w-0 overflow-hidden">
         <div className="shrink-0 h-12 flex items-center px-3 border-b border-border bg-secondary">
           {selectedFile ? (
-            <div className="flex items-center justify-between">
+            <div className="flex items-center justify-between w-full">
               {isRenaming ? (
                 <div className="flex items-center space-x-2 flex-1">
                   <span>{getFileIcon(selectedFile.split('/').pop() || "", false)}</span>