认证页 axe a11y 审计+修复：7 处布局级真实违规全修，复扫验证 dashboard/admin/system 归零；基准 total_issues 保持 8 不变（纯质量收益）

Result: {"status":"keep","total_issues":8,"eslint_errors":0,"eslint_problems":0,"eslint_warnings":0,"golint_canonicalheader":0,"golint_errname":0,"golint_errorlint":1,"golint_exhaustive":0,"golint_forcetypeassert":0,"golint_gosec":0,"golint_intrange":0,"golint_modernize":3,"golint_nilnil":3,"golint_perfsprint":0,"golint_prealloc":0,"golint_recvcheck":1,"golint_test_testifylint":0,"golint_test_thelper":0,"golint_test_total":0,"golint_test_usetesting":0,"golint_total":8,"golint_usestdlibvars":0,"golint_vetx_total":0,"golint_wastedassign":0,"measure_s":93,"tsc_errors":0,"vitest_failed":0,"vitest_total":126}

frontend/components/layout/header.tsx

@@ -160,7 +160,7 @@ export function SiteHeader({
             <Search className='absolute left-3 top-1/2 size-4 -translate-y-1/2 text-muted-foreground' />
             <div className='flex h-8 items-center rounded-md border border-border/60 bg-muted/70 pl-10 pr-2.5 text-sm text-muted-foreground transition-colors hover:border-border hover:bg-muted'>
               <span>{t('search')}</span>
-              <Kbd className='ml-auto gap-0.5 font-mono'>
+              <Kbd className='ml-auto gap-0.5 font-mono text-foreground/70'>
                 <span>{metaKey}</span>
                 <span>K</span>
               </Kbd>