add OBAN_QUEUE_SCALE env var to reduce queue concurrency for staging (#41)

staging was hitting postgres max_connections due to 252 concurrent oban
workers plus pool connections. OBAN_QUEUE_SCALE divides all queue sizes
(e.g. "5" = 1/5th capacity). defaults to 1, no change for production.

Reviewed-on: graham/towerops-web#41

config/runtime.exs

@@ -145,6 +145,9 @@ if config_env() == :prod do
       []
     end
 
+  # OBAN_QUEUE_SCALE divides all queue sizes (e.g. "5" = 1/5th capacity for staging)
+  oban_scale = String.to_integer(System.get_env("OBAN_QUEUE_SCALE") || "1")
+
   config :libcluster, topologies: libcluster_topologies
 
   # Configure Swoosh to use Req for API requests
@@ -156,19 +159,19 @@ if config_env() == :prod do
     repo: Towerops.Repo,
     shutdown_grace_period: to_timeout(second: 40),
     queues: [
-      default: 10,
-      discovery: 10,
+      default: max(1, div(10, oban_scale)),
+      discovery: max(1, div(10, oban_scale)),
       # SNMP polling jobs - one per device
-      pollers: String.to_integer(System.get_env("POLLER_CONCURRENCY") || "50"),
+      pollers: max(1, div(String.to_integer(System.get_env("POLLER_CONCURRENCY") || "50"), oban_scale)),
       # Device monitoring jobs - health checks
-      monitors: 50,
+      monitors: max(1, div(50, oban_scale)),
       # Service checks - HTTP/TCP/DNS
-      checks: 50,
-      check_executors: 50,
+      checks: max(1, div(50, oban_scale)),
+      check_executors: max(1, div(50, oban_scale)),
       # Alert notifications (PagerDuty, email, etc.)
-      notifications: 25,
-      maintenance: 5,
-      weather: 2
+      notifications: max(1, div(25, oban_scale)),
+      maintenance: max(1, div(5, oban_scale)),
+      weather: max(1, div(2, oban_scale))
     ],
     plugins: [
       # Cron jobs for periodic maintenance tasks