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/migrations/0064_security_event_connection_idempotency_repair.sql

@@ -0,0 +1,15 @@
+-- 0063 was released before its idempotency table was added. Installations that
+-- already recorded 0063 need a new immutable migration to repair that drift.
+CREATE TABLE IF NOT EXISTS gateway_security_event_connection_idempotency (
+  operation text NOT NULL,
+  idempotency_key text NOT NULL,
+  request_hash text NOT NULL,
+  response jsonb NOT NULL,
+  created_at timestamptz NOT NULL DEFAULT now(),
+  PRIMARY KEY (operation, idempotency_key),
+  CONSTRAINT gateway_security_event_connection_idempotency_operation
+    CHECK (operation IN ('connect','verify','rotate','disconnect'))
+);
+
+CREATE INDEX IF NOT EXISTS idx_gateway_security_event_connection_idempotency_created
+  ON gateway_security_event_connection_idempotency(created_at);