test(galaxy): de-flake writer-lane and supervisor tests; align EffectiveTimeout doc

The writer concurrency fake parks on its release signal (the 300 ms delay could release the
gate early on a starved pool), the supervisor test's cross-thread hold flag is Volatile, and
the EffectiveTimeout doc now states the 1 s floor the code and tests implement.

Refs #735

Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriverProbe.cs

@@ -165,7 +165,9 @@ public sealed class GalaxyDriverProbe : IDriverProbe
     ///     config's <see cref="GalaxyDriverOptions.ProbeTimeoutSeconds"/> when that is positive and
     ///     shorter. The knob was authored by the AdminUI and parsed by the factory but consumed by
     ///     nothing — the probe always ran on the caller's budget alone. A non-positive caller budget
-    ///     is treated as the config value (or 1 s when that is unset too), as before.
+    ///     is floored to 1 s before the comparison (the same floor <see cref="BuildProbeClientOptions"/>
+    ///     applies to the gRPC call budget), so the probe runs briefly rather than cancelling before
+    ///     it starts; a longer config value never raises it above that floor.
     /// </summary>
     /// <param name="callerTimeout">The budget the host handed the probe.</param>
     /// <param name="configuredSeconds">The config's <c>ProbeTimeoutSeconds</c>; ignored when not positive.</param>