Add strict typespecs to all Oban worker perform/1 functions

Adds @spec annotations to all Oban worker perform/1 functions to improve
static analysis and documentation. Return types are specific to each worker's
actual behavior:

Workers returning 🆗
- BackupSummaryWorker
- BackupTimeoutWorker
- DeviceMonitorWorker
- DevicePollerWorker
- JobHealthCheckWorker
- NeighborCleanupWorker

Workers with complex returns:
- DiscoveryWorker: :ok | :discard
- FirmwareVersionFetcherWorker: :ok | {:error, term()}
- LoginHistoryCleanupWorker: {:ok, %{deleted: non_neg_integer(), anonymized_deleted: non_neg_integer()}}
- MikrotikBackupWorker: :ok | {:error, String.t()}
- SessionCleanupWorker: {:ok, %{sessions_deleted: non_neg_integer()}}

Analysis found that none of these workers have complex job parameters that
would benefit from embedded schemas - all use either no parameters or simple
device_id strings passed in job args.

StaleAgentWorker already had a typespec on find_stale_agents/0 from previous work.

All 98 worker tests passing after changes.

lib/towerops/snmp/neighbor_cleanup_worker.ex

@@ -19,6 +19,7 @@ defmodule Towerops.Snmp.NeighborCleanupWorker do
   @stale_threshold_hours 24
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok
   def perform(%Oban.Job{}) do
     cleanup_stale_records()
     :ok

lib/towerops/workers/backup_summary_worker.ex

@@ -13,6 +13,7 @@ defmodule Towerops.Workers.BackupSummaryWorker do
   require Logger
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok
   def perform(%Oban.Job{}) do
     yesterday = DateTime.add(DateTime.utc_now(), -24 * 60 * 60, :second)
 

lib/towerops/workers/backup_timeout_worker.ex

@@ -16,6 +16,7 @@ defmodule Towerops.Workers.BackupTimeoutWorker do
   @timeout_minutes 5
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok
   def perform(%Oban.Job{}) do
     cutoff = DateTime.add(DateTime.utc_now(), -@timeout_minutes * 60, :second)
     timeout_count = BackupRequests.mark_timed_out_requests(cutoff)

lib/towerops/workers/device_monitor_worker.ex

@@ -28,6 +28,7 @@ defmodule Towerops.Workers.DeviceMonitorWorker do
   @monitor_interval 30
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok
   def perform(%Oban.Job{args: %{"device_id" => device_id}}) do
     case Devices.get_device(device_id) do
       nil ->

lib/towerops/workers/device_poller_worker.ex

@@ -34,6 +34,7 @@ defmodule Towerops.Workers.DevicePollerWorker do
   @default_poll_interval 60
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok
   def perform(%Oban.Job{args: %{"device_id" => device_id}}) do
     case Devices.get_device(device_id) do
       nil ->

lib/towerops/workers/discovery_worker.ex

@@ -38,6 +38,7 @@ defmodule Towerops.Workers.DiscoveryWorker do
   @agent_online_threshold_minutes 10
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok | :discard
   def perform(%Oban.Job{args: %{"device_id" => device_id}}) do
     case Devices.get_device_with_details(device_id) do
       nil ->

lib/towerops/workers/firmware_version_fetcher_worker.ex

@@ -17,6 +17,7 @@ defmodule Towerops.Workers.FirmwareVersionFetcherWorker do
   @changelog_url "https://mikrotik.com/download/changelogs"
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok | {:error, term()}
   def perform(%Oban.Job{}) do
     Logger.info("Fetching MikroTik RouterOS firmware version from RSS feed")
 

lib/towerops/workers/job_health_check_worker.ex

@@ -23,6 +23,7 @@ defmodule Towerops.Workers.JobHealthCheckWorker do
   require Logger
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok
   def perform(%Oban.Job{}) do
     monitor_recoveries = recover_missing_monitor_jobs()
     poller_recoveries = recover_missing_poller_jobs()

lib/towerops/workers/login_history_cleanup_worker.ex

@@ -16,6 +16,7 @@ defmodule Towerops.Workers.LoginHistoryCleanupWorker do
   alias Towerops.Repo
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: {:ok, %{deleted: non_neg_integer(), anonymized_deleted: non_neg_integer()}}
   def perform(_job) do
     # Delete login attempts older than retention period (365 days)
     retention_days = Application.get_env(:towerops, :login_history_retention_days, 365)

lib/towerops/workers/mikrotik_backup_worker.ex

@@ -23,6 +23,7 @@ defmodule Towerops.Workers.MikrotikBackupWorker do
   require Logger
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: :ok | {:error, String.t()}
   def perform(%Oban.Job{}) do
     Logger.info("Starting MikroTik configuration backup job")
 

lib/towerops/workers/session_cleanup_worker.ex

@@ -10,6 +10,7 @@ defmodule Towerops.Workers.SessionCleanupWorker do
   alias Towerops.Accounts
 
   @impl Oban.Worker
+  @spec perform(Oban.Job.t()) :: {:ok, %{sessions_deleted: non_neg_integer()}}
   def perform(_job) do
     count = Accounts.delete_expired_browser_sessions()
     {:ok, %{sessions_deleted: count}}