Change agent mode token enablement flag (microsoft#258700)

https://docs.google.com/document/d/1PX9E-UaNqhgisVjwVmo4YmsP1tSIJVDRonMt7IGxOkM/edit?tab=t.0

Author: roblourens

src/vs/workbench/services/accounts/common/defaultAccount.ts

@@ -251,7 +251,7 @@ export class DefaultAccountManagementContribution extends Disposable implements
 				return {
 					// Editor preview features are disabled if the flag is present and set to 0
 					chat_preview_features_enabled: tokenMap.get('editor_preview_features') !== '0',
-					chat_agent_enabled: tokenMap.get('chat_agent_enabled') !== '0',
+					chat_agent_enabled: tokenMap.get('agent_mode') !== '0',
 					// MCP is disabled if the flag is present and set to 0
 					mcp: tokenMap.get('mcp') !== '0',
 				};