feat(agent): persist 7-day metrics history per server heartbeat

- New table servidor_metricas_history (cpu%, ram%, swap%, disco%, tcp, load1)
- Each heartbeat inserts a compact row (~60 bytes)
- GET /app/servidor/:id/metricas-history?horas=24 returns the data
- Daily cron at 3AM purges rows older than 7 days
- ~1.2 MB per server per 7 days at 30s interval

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rest/controllers/agent_controller.go

@@ -89,9 +89,75 @@ func AgentHeartbeat(c *fiber.Ctx) error {
 		return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"ok": false, "error": "no se pudo guardar"})
 	}
 
+	// Insertar punto en el historial de métricas
+	if req.Metricas != "" {
+		var raw map[string]any
+		if json.Unmarshal([]byte(req.Metricas), &raw) == nil {
+			getFloat := func(obj map[string]any, key string) float64 {
+				if sub, ok := obj[key].(map[string]any); ok {
+					if v, ok := sub["porcentaje"].(float64); ok {
+						return v
+					}
+				}
+				return 0
+			}
+			discoPct := 0.0
+			if discos, ok := raw["discos"].([]any); ok && len(discos) > 0 {
+				if d, ok := discos[0].(map[string]any); ok {
+					if v, ok := d["porcentaje"].(float64); ok {
+						discoPct = v
+					}
+				}
+			}
+			tcpConns := 0
+			if v, ok := raw["tcp_conns"].(float64); ok {
+				tcpConns = int(v)
+			}
+			load1 := 0.0
+			if la, ok := raw["load_avg"].(map[string]any); ok {
+				if v, ok := la["load1"].(float64); ok {
+					load1 = v
+				}
+			}
+			swapPct := 0.0
+			if sw, ok := raw["swap"].(map[string]any); ok {
+				if v, ok := sw["porcentaje"].(float64); ok {
+					swapPct = v
+				}
+			}
+			models.InsertMetricasHistory(servidor.ID,
+				getFloat(raw, "cpu"),
+				getFloat(raw, "ram"),
+				swapPct,
+				discoPct,
+				tcpConns,
+				load1,
+			)
+		}
+	}
+
 	return c.JSON(fiber.Map{"ok": true, "servidor_id": servidor.ID})
 }
 
+// GetMetricasHistory devuelve el historial de métricas de un servidor.
+// GET /app/servidor/:id/metricas-history?horas=24
+func GetMetricasHistory(c *fiber.Ctx) error {
+	id := c.Params("id")
+	horas := c.QueryInt("horas", 24)
+	if horas <= 0 || horas > 168 {
+		horas = 24
+	}
+	var srv models.Servidor
+	if err := app.Http.Database.DB.First(&srv, id).Error; err != nil {
+		return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "servidor no encontrado"})
+	}
+	items, err := models.GetMetricasHistory(srv.ID, horas)
+	if err != nil {
+		return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
+	}
+	return c.JSON(items)
+}
+
 // GenerateAgentToken genera o regenera el token de agente para un servidor.
 // Ruta protegida: POST /app/servidor/:id/agent-token
 func GenerateAgentToken(c *fiber.Ctx) error {