Switch Oban to the Pro Smart engine, rate-limit ERA5 CDS

Wire up the Oban Pro Smart engine in base + runtime config and add the
Pro migration (oban_producers, oban_crons, oban_queues tables + the
v1.6 partition/workflow index additions on oban_jobs).

On the Smart engine the era5_batch queue now has a global_limit of 4
in-flight jobs across the cluster and a rate_limit of 10 jobs per hour
so slow Copernicus CDS submit/poll cycles can't exhaust our daily
request budget when a backfill kicks off.

config/config.exs

@@ -43,6 +43,7 @@ config :microwaveprop, MicrowavepropWeb.Endpoint,
   live_view: [signing_salt: "Gdq36xze"]
 
 config :microwaveprop, Oban,
+  engine: Oban.Pro.Engines.Smart,
   repo: Microwaveprop.Repo,
   queues: [solar: 1, weather: 20, enqueue: 1, hrrr: 5, terrain: 4, commercial: 2, iemre: 10, propagation: 1],
   plugins: [

config/runtime.exs

@@ -129,8 +129,11 @@ if config_env() == :prod do
     ],
     secret_key_base: secret_key_base
 
-  # Production Oban: live scoring, polling, and on-demand QSO enrichment
+  # Production Oban: live scoring, polling, and on-demand QSO enrichment.
+  # Runs on the Oban Pro Smart engine so we can use global_limit / rate_limit
+  # to protect rate-limited upstreams (Copernicus CDS in particular).
   config :microwaveprop, Oban,
+    engine: Oban.Pro.Engines.Smart,
     # Per-pod concurrency (×3 pods = effective cluster total)
     queues: [
       propagation: 1,
@@ -141,7 +144,11 @@ if config_env() == :prod do
       terrain: 3,
       iemre: 3,
       era5: 2,
-      era5_batch: 2,
+      era5_batch: [
+        local_limit: 2,
+        global_limit: 4,
+        rate_limit: [allowed: 10, period: {1, :hour}]
+      ],
       rtma: 2,
       backfill_enqueue: 1
     ],

priv/repo/migrations/20260409191733_add_oban_pro.exs

@@ -0,0 +1,7 @@
+defmodule Microwaveprop.Repo.Migrations.AddObanPro do
+  use Ecto.Migration
+
+  def up, do: Oban.Pro.Migration.up()
+
+  def down, do: Oban.Pro.Migration.down()
+end