fix: respect device SNMP version for agent polling instead of forcing v2c (#166)

Devices configured as SNMPv1 were being force-upgraded to v2c for agent
polling, which breaks devices that don't support v2c (returning empty
OID responses and no throughput/capacity data).

Reviewed-on: graham/towerops-web#166

lib/towerops_web/channels/agent_channel.ex

@@ -1083,14 +1083,17 @@ defmodule ToweropsWeb.AgentChannel do
   defp build_v2c_snmp_device(device, snmp_config) do
     community = snmp_config.community || ""
 
-    # Always use v2c for agent polling — Counter64 (HC counters) can't be
-    # encoded in SNMPv1 responses, causing 64-bit counter queries to fail.
-    # v2c uses the same community string and is supported by virtually all
-    # SNMP-capable devices. Without HC counters, 32-bit counters on fast
-    # links wrap undetectably (full cycle in ~69s at 500 Mbps).
+    # Use v2c when possible for HC (64-bit) counter support, but respect
+    # the device's configured version — some devices only support v1.
+    version =
+      case device.snmp_version do
+        "1" -> "1"
+        _ -> "2c"
+      end
+
     %SnmpDevice{
       ip: device.ip_address,
-      version: "2c",
+      version: version,
       port: device.snmp_port || 161,
       community: community
     }