docs(overview): correct fixture gap expectation

中文：修正总览页 fixture 的第二名差距预期。

Author: edwingao28

docs/superpowers/plans/2026-07-21-executive-overview.md

@@ -748,7 +748,7 @@ describe('Executive overview', () => {
     cy.contains('tr', 'DeepSeek V4 Pro').within(() => {
       cy.contains('Best').should('exist');
       cy.contains('1,200').should('exist');
-      cy.contains('+20%').should('exist');
+      cy.contains('+25%').should('exist');
     });
   });