fix(backfill): cap cron run at 2000 contacts/tick to avoid 17 min discard

Unlimited BackfillEnqueueWorker runs loaded all ~36k enrichable
contacts and hit Oban's ~17 min execution timeout, discarding the
parent job every cron tick. Enrichment was landing partially
(jobs enqueued before the timeout) but the loop never completed
and no success signal was emitted. A per-tick limit of 2000 keeps
each run well under any timeout while still draining the backlog
at 4000/hour across the */30 schedule.

config/runtime.exs

@@ -208,8 +208,15 @@ if config_env() == :prod do
        # The :narr type is virtual: it targets contacts with hrrr_status =
        # :unavailable (pre-2014, missing from the HRRR archive) and dispatches
        # NarrFetchWorker against NCEI. See narr_jobs_for_contact/1.
+       # limit=2000 keeps each 30-min tick under the Oban job-execution
+       # timeout that discards unlimited runs after ~17 min. At 4000
+       # contacts/hour the backlog of missing-data contacts drains
+       # steadily without any single job getting killed mid-way.
        {"*/30 * * * *", Microwaveprop.Workers.BackfillEnqueueWorker,
-        args: %{"types" => ["hrrr", "weather", "terrain", "iemre", "narr", "radar", "mechanism"]}},
+        args: %{
+          "limit" => 2000,
+          "types" => ["hrrr", "weather", "terrain", "iemre", "narr", "radar", "mechanism"]
+        }},
        # Hourly safety net for pos1/pos2/distance_km. Normally every contact
        # gets positions at insert time via Radio.resolve_grids_and_insert/1,
        # but direct DB writes (manual fixes, bulk imports) can bypass that.