fix(prune): widen profile/score file cutoff from 2h to 3h

HRRR publishes ~2h after the cycle hour, so the hourly seeder uses
run_time = now - 2h. That puts the f00 analysis file's valid_time
right at the 2h prune cutoff — the file was being deleted within
minutes of the Rust analysis step writing it, leaving /weather and
/map point-detail with no data.

A 3h cutoff keeps the current analysis alive until the next hourly
run supersedes it; forecast files (valid_time >> cutoff) are
unaffected.

lib/microwaveprop/propagation.ex

@@ -198,12 +198,18 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc """
-  Remove score files with valid_times older than 2 hours. Called on
+  Remove score files with valid_times older than 3 hours. Called on
   a cron by `Microwaveprop.Workers.PropagationPruneWorker`.
+
+  The cutoff sits one hour beyond HRRR's ~2h publish lag: the hourly
+  seeder picks `run_time = now - 2h`, so the f00 analysis file is
+  written at valid_time = now - 2h. A 2h cutoff deletes it within
+  minutes; a 3h cutoff keeps it alive until the next hourly run
+  supersedes it.
   """
   @spec prune_old_scores() :: :ok
   def prune_old_scores do
-    cutoff = DateTime.add(DateTime.utc_now(), -2, :hour)
+    cutoff = DateTime.add(DateTime.utc_now(), -3, :hour)
     file_deleted = ScoresFile.prune_older_than(cutoff)
     profiles_deleted = ProfilesFile.prune_older_than(cutoff)