fix(test): weather_map_live one-hour-cutoff test flake

The test computed recent_t = (truncated_to_top_of_hour now) - 30min,
which is 30-90 min before real utc_now() depending on what minute the
test runs at. The LiveView's `cutoff = utc_now() - 1h` then dropped
recent_t whenever the real-time minute exceeded ~30, so the test
failed half the time.

Anchor recent_t at the top of the current hour — that's always within
the 1-hour window regardless of minute. The test still exercises the
"keep within last hour" path; just stops being clock-flaky.

test/microwaveprop_web/live/weather_map_live_test.exs

@@ -83,7 +83,12 @@ defmodule MicrowavepropWeb.WeatherMapLiveTest do
         |> Map.put(:second, 0)
 
       stale_t = DateTime.add(now, -2 * 3600, :second)
-      recent_t = DateTime.add(now, -30 * 60, :second)
+      # `now` is truncated to the top of the hour; real `utc_now()` is up to
+      # 60 min ahead of that, so a `now - 30 min` recent_t is 30-90 min old
+      # of real time and the LiveView's `utc_now() - 1h` cutoff filters it
+      # out 50% of the time. Anchor recent_t at the top of the current hour
+      # — that's always within the 1-hour window regardless of minute.
+      recent_t = now
       future_t = DateTime.add(now, 3 * 3600, :second)
 
       Enum.each([stale_t, recent_t, future_t], &write_profile(&1, 33.0, -97.0))