Fix database connection ownership issues in async Tasks

Changes:
- ApiTokens.update_last_used/1: Allow Task to access sandbox in tests
- DeviceMonitor.enqueue_check/1: Allow Task to access sandbox in tests
- PollerWorker.enqueue_poll/1: Allow Task to access sandbox in tests

Problem:
When tests spawn async Tasks that access the database, those Tasks
don't have ownership of the database connection in Sandbox mode,
causing DBConnection.ConnectionError warnings.

Solution:
Before accessing the database in a Task, check if we're in test mode
and call Ecto.Adapters.SQL.Sandbox.allow/3 to transfer connection
ownership from the parent process to the Task.

Pattern used:
```elixir
parent = self()
Task.start(fn ->
  if Application.get_env(:towerops, :sql_sandbox) do
    Ecto.Adapters.SQL.Sandbox.allow(Repo, parent, self())
  end
  # ... database operations ...
end)
```

All 1041 tests passing. Some harmless disconnection warnings remain
when Tasks complete after tests finish, but these don't affect results.

lib/towerops/api_tokens.ex

@@ -172,9 +172,17 @@ defmodule Towerops.ApiTokens do
   end
 
   defp update_last_used(token) do
+    # Get the parent process PID before spawning the task
+    parent = self()
+
     # Use Task.start to avoid blocking the request
     # We don't care if this fails
     Task.start(fn ->
+      # Allow the task to access the database in test mode
+      if Application.get_env(:towerops, :sql_sandbox) do
+        Ecto.Adapters.SQL.Sandbox.allow(Repo, parent, self())
+      end
+
       token
       |> Ecto.Changeset.change(last_used_at: DateTime.truncate(DateTime.utc_now(), :second))
       |> Repo.update()

lib/towerops/monitoring/device_monitor.ex

@@ -7,6 +7,7 @@ defmodule Towerops.Monitoring.DeviceMonitor do
   alias Towerops.Alerts
   alias Towerops.Devices
   alias Towerops.Monitoring
+  alias Towerops.Repo
 
   require Logger
 
@@ -219,8 +220,16 @@ defmodule Towerops.Monitoring.DeviceMonitor do
   # Enqueue monitoring check job - safe to call in test environment
   defp enqueue_check(device_id) do
     if Application.get_env(:towerops, :env) == :test do
-      # In test, run synchronously
-      Task.start(fn -> perform_check(device_id) end)
+      # In test, run synchronously with database sandbox access
+      parent = self()
+
+      Task.start(fn ->
+        if Application.get_env(:towerops, :sql_sandbox) do
+          Ecto.Adapters.SQL.Sandbox.allow(Repo, parent, self())
+        end
+
+        perform_check(device_id)
+      end)
     else
       # In dev/prod, enqueue to Exq
       {:ok, _job} = Exq.enqueue(Exq, "monitoring", Towerops.Workers.MonitorWorker, [device_id])

lib/towerops/snmp/poller_worker.ex

@@ -1066,8 +1066,16 @@ defmodule Towerops.Snmp.PollerWorker do
   # Enqueue poll job - safe to call in test environment
   defp enqueue_poll(device_id) do
     if Application.get_env(:towerops, :env) == :test do
-      # In test, run synchronously
-      Task.start(fn -> perform_poll(device_id) end)
+      # In test, run synchronously with database sandbox access
+      parent = self()
+
+      Task.start(fn ->
+        if Application.get_env(:towerops, :sql_sandbox) do
+          Ecto.Adapters.SQL.Sandbox.allow(Repo, parent, self())
+        end
+
+        perform_poll(device_id)
+      end)
     else
       # In dev/prod, enqueue to Exq
       {:ok, _job} = Exq.enqueue(Exq, "polling", Towerops.Workers.PollWorker, [device_id])