Add ICMP monitoring support to Phoenix agent channel

- Add monitoring_enabled and check_interval_seconds fields to Device and SnmpDevice protobuf messages
- Add MonitoringCheck protobuf message for ping results
- Update AgentChannel to handle monitoring_check events from agents
- Configure monitoring settings in job payloads sent to agents

lib/towerops/proto/agent.pb.ex

@@ -26,6 +26,8 @@ defmodule Towerops.Agent.Device do
   field :poll_interval_seconds, 5, type: :uint32, json_name: "pollIntervalSeconds"
   field :sensors, 6, repeated: true, type: Towerops.Agent.Sensor
   field :interfaces, 7, repeated: true, type: Towerops.Agent.Interface
+  field :monitoring_enabled, 8, type: :bool, json_name: "monitoringEnabled"
+  field :check_interval_seconds, 9, type: :uint32, json_name: "checkIntervalSeconds"
 end
 
 defmodule Towerops.Agent.SnmpConfig do
@@ -119,6 +121,11 @@ defmodule Towerops.Agent.Metric do
     type: Towerops.Agent.NeighborDiscovery,
     json_name: "neighborDiscovery",
     oneof: 0
+
+  field :monitoring_check, 4,
+    type: Towerops.Agent.MonitoringCheck,
+    json_name: "monitoringCheck",
+    oneof: 0
 end
 
 defmodule Towerops.Agent.SensorReading do
@@ -174,6 +181,20 @@ defmodule Towerops.Agent.NeighborDiscovery do
   field :timestamp, 11, type: :int64
 end
 
+defmodule Towerops.Agent.MonitoringCheck do
+  @moduledoc false
+
+  use Protobuf,
+    full_name: "towerops.agent.MonitoringCheck",
+    protoc_gen_elixir_version: "0.16.0",
+    syntax: :proto3
+
+  field :device_id, 1, type: :string, json_name: "deviceId"
+  field :status, 2, type: :string
+  field :response_time_ms, 3, type: :double, json_name: "responseTimeMs"
+  field :timestamp, 4, type: :int64
+end
+
 defmodule Towerops.Agent.HeartbeatMetadata do
   @moduledoc false
 
@@ -262,6 +283,8 @@ defmodule Towerops.Agent.SnmpDevice do
   field :community, 2, type: :string
   field :version, 3, type: :string
   field :port, 4, type: :uint32
+  field :monitoring_enabled, 5, type: :bool, json_name: "monitoringEnabled"
+  field :check_interval_seconds, 6, type: :uint32, json_name: "checkIntervalSeconds"
 end
 
 defmodule Towerops.Agent.SnmpQuery do

priv/proto/agent.proto

@@ -17,6 +17,8 @@ message Device {
   uint32 poll_interval_seconds = 5;
   repeated Sensor sensors = 6;
   repeated Interface interfaces = 7;
+  bool monitoring_enabled = 8;
+  uint32 check_interval_seconds = 9;
 }
 
 message SnmpConfig {
@@ -51,6 +53,7 @@ message Metric {
     SensorReading sensor_reading = 1;
     InterfaceStat interface_stat = 2;
     NeighborDiscovery neighbor_discovery = 3;
+    MonitoringCheck monitoring_check = 4;
   }
 }
 
@@ -86,6 +89,13 @@ message NeighborDiscovery {
   int64 timestamp = 11; // Unix timestamp in seconds
 }
 
+message MonitoringCheck {
+  string device_id = 1;
+  string status = 2; // "success" or "failure"
+  double response_time_ms = 3; // Optional - only present on success
+  int64 timestamp = 4; // Unix timestamp in seconds
+}
+
 // Heartbeat metadata
 message HeartbeatMetadata {
   string version = 1;
@@ -126,6 +136,8 @@ message SnmpDevice {
   string community = 2;
   string version = 3;  // "1", "2c", or "3"
   uint32 port = 4;
+  bool monitoring_enabled = 5;
+  uint32 check_interval_seconds = 6;
 }
 
 message SnmpQuery {