auto-claude: subtask-1-1 - Remove Reference Files toggle button

Remove the 'Reference Files (optional)' toggle button that controlled
the showFiles state for the collapsible section. The FolderTree icon
toggle with chevron is now removed from TaskCreationWizard.tsx.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

auto-claude-ui/src/renderer/components/TaskCreationWizard.tsx

@@ -746,32 +746,6 @@ export function TaskCreationWizard({
             </div>
           )}
 
-          {/* Reference Files Toggle */}
-          <button
-            type="button"
-            onClick={() => setShowFiles(!showFiles)}
-            className={cn(
-              'flex items-center gap-2 text-sm text-muted-foreground hover:text-foreground transition-colors',
-              'w-full justify-between py-2 px-3 rounded-md hover:bg-muted/50'
-            )}
-            disabled={isCreating}
-          >
-            <span className="flex items-center gap-2">
-              <FolderTree className="h-4 w-4" />
-              Reference Files (optional)
-              {referencedFiles.length > 0 && (
-                <span className="text-xs bg-primary/10 text-primary px-1.5 py-0.5 rounded">
-                  {referencedFiles.length}
-                </span>
-              )}
-            </span>
-            {showFiles ? (
-              <ChevronUp className="h-4 w-4" />
-            ) : (
-              <ChevronDown className="h-4 w-4" />
-            )}
-          </button>
-
           {/* Referenced Files Section - Drop Zone */}
           {showFiles ? (
             <div