feat(gateway): 护栏拦截事件落库 + 安全事件流（T4.B）

- store.GuardrailEvent 表(sundynix_guardrail_event) + AppendGuardrailEvent/ListGuardrailEvents
- middleware.Guardrail(db)：命中 blocked/suspect 时 best-effort 落库
  (actor/kind/reason/signals/method/path/ip，独立超时 ctx)
- GET /api/v1/admin/guardrail-events：安全事件流(倒序，翻页)
- store.clampPage 抽出分页归一(audit/guardrail 共用)
- live：注入 "ignore all previous instructions" → 422 硬拦 + 事件留痕(kind=blocked)
- DEPTH_ROADMAP T4.B 护栏事件打勾

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sundynix-gateway/internal/handler/admin.go

@@ -45,6 +45,34 @@ func (h *Handler) AuditList(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"logs": out})
 }
 
+// GuardrailEvents: GET /api/v1/admin/guardrail-events?limit=&offset= —— 护栏命中安全事件流（倒序）。
+func (h *Handler) GuardrailEvents(c *gin.Context) {
+	limit, offset := 50, 0
+	if v := c.Query("limit"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			limit = n
+		}
+	}
+	if v := c.Query("offset"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			offset = n
+		}
+	}
+	rows, err := h.db.ListGuardrailEvents(c.Request.Context(), limit, offset)
+	if err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": err.Error()})
+		return
+	}
+	out := make([]gin.H, 0, len(rows))
+	for _, e := range rows {
+		out = append(out, gin.H{
+			"id": e.ID, "actor": e.Actor, "kind": e.Kind, "reason": e.Reason,
+			"signals": e.Signals, "method": e.Method, "path": e.Path, "ip": e.IP, "at": e.CreatedAt,
+		})
+	}
+	c.JSON(http.StatusOK, gin.H{"events": out})
+}
+
 // AdminOverview: GET /api/v1/admin/overview —— 管理端系统级聚合（控制塔口径）。
 // 区别于 stats/overview（桌面端个人工作台）：这里一律系统级——全平台用户/任务/评测/
 // 模型配置态/提示词控制面态/服务健康。Task/Eval 表无 owner 即全量；用户/KB/Doc 走全局计数。