refactor: move temperature backfill to a release-safe module

Mix tasks aren't usable from the prod release image — `/app/bin/towerops`
ships without `mix`, and `Mix.shell()` raises at runtime. Move the work
to `Towerops.Maintenance.FixMikrotikTemperatureScaling` (plain module
with `run/0`, IO.puts + Logger.info) and keep the Mix.Task as a thin
dev-only delegator.

Run in prod via:

    /app/bin/towerops eval 'Towerops.Maintenance.FixMikrotikTemperatureScaling.run()'

lib/mix/tasks/towerops.fix_mikrotik_temperature_scaling.ex

@@ -2,57 +2,25 @@ defmodule Mix.Tasks.Towerops.FixMikrotikTemperatureScaling do
   @shortdoc "Renormalise stored temperature sensor readings using SensorScale"
 
   @moduledoc """
-  One-shot backfill that re-runs `Towerops.Snmp.SensorScale.normalize/2`
-  over every stored temperature reading. Catches historical mis-scaled
-  rows from MikroTik `mtxrGaugeValue` (some models report deci-degrees)
-  and any other sensor whose YAML profile didn't include the right
-  divisor at discovery time.
-
-  Run from inside a release pod:
-
-      /app/bin/towerops eval 'Mix.Tasks.Towerops.FixMikrotikTemperatureScaling.run([])'
-
-  Or via mix during dev:
+  Dev-only convenience wrapper. Delegates to
+  `Towerops.Maintenance.FixMikrotikTemperatureScaling.run/0` so you can
+  run the backfill from a local checkout via:
 
       mix towerops.fix_mikrotik_temperature_scaling
+
+  In prod the release has no `mix` binary — invoke the plain module
+  directly:
+
+      /app/bin/towerops eval 'Towerops.Maintenance.FixMikrotikTemperatureScaling.run()'
   """
 
   use Mix.Task
 
-  import Ecto.Query
-
-  alias Towerops.Repo
-  alias Towerops.Snmp.Sensor
-  alias Towerops.Snmp.SensorScale
+  alias Towerops.Maintenance.FixMikrotikTemperatureScaling
 
   @impl Mix.Task
   def run(_argv) do
     {:ok, _} = Application.ensure_all_started(:towerops)
-
-    sensors =
-      Repo.all(
-        from(s in Sensor, where: s.sensor_type == "temperature" and not is_nil(s.last_value) and s.last_value > 150.0)
-      )
-
-    {fixed, skipped} =
-      Enum.reduce(sensors, {0, 0}, fn sensor, {fixed, skipped} ->
-        normalized = SensorScale.normalize(sensor.sensor_type, sensor.last_value)
-
-        if normalized == sensor.last_value do
-          {fixed, skipped + 1}
-        else
-          {:ok, _} =
-            sensor
-            |> Sensor.changeset(%{last_value: Float.round(normalized / 1.0, 2)})
-            |> Repo.update()
-
-          {fixed + 1, skipped}
-        end
-      end)
-
-    Mix.shell().info(
-      "Temperature backfill complete: rescaled #{fixed} rows, " <>
-        "left #{skipped} unchanged."
-    )
+    FixMikrotikTemperatureScaling.run()
   end
 end

lib/towerops/maintenance/fix_mikrotik_temperature_scaling.ex

@@ -0,0 +1,51 @@
+defmodule Towerops.Maintenance.FixMikrotikTemperatureScaling do
+  @moduledoc """
+  One-shot backfill that re-runs `Towerops.Snmp.SensorScale.normalize/2`
+  over every stored temperature reading. Catches historical mis-scaled
+  rows from MikroTik `mtxrGaugeValue` (some models report deci-degrees)
+  and any other sensor whose YAML profile didn't include the right
+  divisor at discovery time.
+
+  Plain module rather than a `Mix.Task` so it can run from the prod
+  Elixir release (where `mix` itself isn't installed):
+
+      /app/bin/towerops eval 'Towerops.Maintenance.FixMikrotikTemperatureScaling.run()'
+  """
+
+  import Ecto.Query
+
+  alias Towerops.Repo
+  alias Towerops.Snmp.Sensor
+  alias Towerops.Snmp.SensorScale
+
+  require Logger
+
+  @spec run() :: :ok
+  def run do
+    sensors =
+      Repo.all(
+        from(s in Sensor, where: s.sensor_type == "temperature" and not is_nil(s.last_value) and s.last_value > 150.0)
+      )
+
+    {fixed, skipped} =
+      Enum.reduce(sensors, {0, 0}, fn sensor, {fixed, skipped} ->
+        normalized = SensorScale.normalize(sensor.sensor_type, sensor.last_value)
+
+        if normalized == sensor.last_value do
+          {fixed, skipped + 1}
+        else
+          {:ok, _} =
+            sensor
+            |> Sensor.changeset(%{last_value: Float.round(normalized / 1.0, 2)})
+            |> Repo.update()
+
+          {fixed + 1, skipped}
+        end
+      end)
+
+    msg = "Temperature backfill complete: rescaled #{fixed} rows, left #{skipped} unchanged."
+    IO.puts(msg)
+    Logger.info(msg)
+    :ok
+  end
+end