Sync terminal selection AI preference (#1441)

Syncs the terminal selection Add to Conversation preference with AI settings so cloud sync, local backups, restores, and settings-only auto-sync detect the value.

Follow-up for #1436.

domain/sync.ts

@@ -273,6 +273,7 @@ export interface SyncPayload {
       agentProviderMap?: Record<string, string>;
       webSearchConfig?: Record<string, unknown> | null;
       quickMessages?: Array<Record<string, unknown>>;
+      showTerminalSelectionAction?: boolean;
     };
   };