fix(ssf): 修复安全事件连接基础阻断

为已记录旧迁移版本的环境补充幂等表修复迁移，并让 Transmitter 网络连接在 IPv6 地址不可达时继续尝试 IPv4。失败连接现在通过 If-Match 安全重试，页面同步提供重试入口并清理过期错误提示。\n\n验证：Go securityevents/migrate 测试、Web Vitest 与 TypeScript 类型检查通过。

apps/api/cmd/migrate/main_test.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestSecurityEventIdempotencyRepairMigrationExists(t *testing.T) {
+	payload, err := os.ReadFile("../../migrations/0064_security_event_connection_idempotency_repair.sql")
+	if err != nil {
+		t.Fatalf("read repair migration: %v", err)
+	}
+	sql := string(payload)
+	for _, statement := range []string{
+		"CREATE TABLE IF NOT EXISTS gateway_security_event_connection_idempotency",
+		"CREATE INDEX IF NOT EXISTS idx_gateway_security_event_connection_idempotency_created",
+	} {
+		if !strings.Contains(sql, statement) {
+			t.Fatalf("repair migration is missing %q", statement)
+		}
+	}
+}