buildx(history): add platform in summary struct

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

src/buildx/history.ts

@@ -130,6 +130,7 @@ export class History {
             numCachedSteps: res.NumCachedSteps,
             numTotalSteps: res.NumTotalSteps,
             numCompletedSteps: res.NumCompletedSteps,
+            defaultPlatform: res.Platform?.[0],
             error: errorLogs
           };
         });

src/types/buildx/history.ts

@@ -131,5 +131,6 @@ export interface Summary {
   numTotalSteps: number;
   numCompletedSteps: number;
   frontendAttrs?: Record<string, string>;
+  defaultPlatform?: string;
   error?: string;
 }