docs(mqtt): flag the Last-Will landmine at the browse-options seam

A will is published by the BROKER, so it is invisible to PublishCountForTest.
MqttDriverOptions carries none today, but Sparkplug NDEATH is a will message -
once P2 adds it, an ungraceful browse disconnect would fire NDEATH under the
plant's own edge-node identity. ToBrowseOptions is where it must be cleared.

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser/MqttDriverBrowser.cs

@@ -154,6 +154,15 @@ public sealed class MqttDriverBrowser : IDriverBrowser
     ///     Projects the authored options into the ones the browse CONNECT uses. Clean session is
     ///     forced: a transient browse identity must not leave queued-message state behind on the
     ///     broker after the picker closes.
+    ///     <para>
+    ///         ⚠ <b>P2 landmine — a Last Will would break the read-only guarantee from outside it.</b>
+    ///         <c>MqttDriverOptions</c> carries no will today, so there is nothing to strip. When the
+    ///         Sparkplug tasks add one (NDEATH <i>is</i> a will message), it MUST be cleared here: a
+    ///         will is published by the <i>broker</i>, not by us, so it is invisible to
+    ///         <see cref="MqttBrowseSession.PublishCountForTest"/> — and any ungraceful end to a browse
+    ///         session (crash, dropped link, the disconnect deadline expiring) would then fire an
+    ///         NDEATH under the plant's own edge-node identity.
+    ///     </para>
     /// </summary>
     /// <param name="options">The authored configuration.</param>
     /// <returns>The configuration the browse CONNECT is built from.</returns>