后端与全仓代码质量清理（golangci 扩展集 · 测试质量 · 并发安全 · 文档同步）

代码质量全量清理，零行为变化：golangci 扩展集 13 类 linter（gosec/modernize/perfsprint/canonicalheader/usestdlibvars/wastedassign/intrange/errorlint/forcetypeassert/recvcheck/exhaustive/unparam）全量修复，测试代码质量（testifylint/thelper/usetesting）25→0，frpc 进程生命周期真 bug（进程组击杀）、全仓 go test -race 6 类数据竞争（含 1 个生产竞争）、SPDX license 头补齐 131 文件、前端测试套件 next-intl 迁移后 44 失败→全绿、过期 swagger 文档重新生成、pnpm-workspace 构建审批。

Experiments: #2-#17, #18, #20, #21, #23
Metric: total_issues 108 → 8 (-92.6%)

internal/infra/persistence/migrator/pages_source_migration_test.go

@@ -198,7 +198,7 @@ func assertPagesSourceConstraints(t *testing.T, gormDB *gorm.DB, sourceID uint)
 		ConfigVersion:  1,
 		SourceIdentity: strings.Repeat("c", 64),
 	}
-	assert.Error(t, gormDB.Create(&duplicateSource).Error)
+	require.Error(t, gormDB.Create(&duplicateSource).Error)
 
 	for number := 2; number <= 3; number++ {
 		require.NoError(t, createMigrationDeployment(
@@ -219,14 +219,14 @@ func assertPagesSourceConstraints(t *testing.T, gormDB *gorm.DB, sourceID uint)
 		&identity,
 		&revision,
 	))
-	assert.Error(t, createMigrationDeployment(
+	require.Error(t, createMigrationDeployment(
 		gormDB,
 		5,
 		strings.Repeat("0", 64),
 		&identity,
 		&revision,
 	))
-	assert.Error(t, createMigrationDeployment(
+	require.Error(t, createMigrationDeployment(
 		gormDB,
 		1,
 		strings.Repeat("1", 64),