feat(mqtt): Sparkplug birth-driven browser tree + scoped Request-rebirth action

Unseals the Sparkplug branch of the MQTT address-picker browser that Task 10
deliberately sealed shut, and adds the first (and only) sanctioned publish on a
browse session.

- MqttBrowseSession serves Group -> EdgeNode -> [Device] -> Metric in Sparkplug
  mode, decoded from observed NBIRTH/DBIRTH certificates (the only Sparkplug
  messages that name their metrics). Node-level metrics hang directly under
  their edge node -- no synthesised device folder, because the authored address
  tuple genuinely has deviceId = null for them. Metric node ids use a '::'
  separator: a metric name may contain '/', so slash-joining would make a
  node-level metric indistinguishable from a device folder.
- AttributesAsync is purely birth-derived in Sparkplug mode. The plain path's
  UTF-8 inference / payload-snippet machinery does not run and no payload bytes
  are retained: a Sparkplug body is protobuf and would be reported as
  "(N bytes, binary)" for every metric in the plant. A datatype ToDriverDataType
  cannot map is reported as the Sparkplug type name, never coerced.
- RequestRebirthAsync(scope) is the one publishing member, reached only by an
  explicit operator action. It routes through the counted PublishAsync
  chokepoint via a private RebirthTransport adapter, so PublishCountForTest
  still proves that OpenAsync/RootAsync/ExpandAsync/AttributesAsync/Observe/
  DisposeAsync publish nothing -- now in both modes. A device or metric scope
  resolves up to its owning edge node (NCMD is node-addressed); group scope
  enumerates observed edge nodes and is refused whole past
  MaxGroupRebirthNodes = 32.
- BrowserSessionService.RequestRebirthAsync gates on the same DriverOperator
  policy that gates the picker, evaluated server-side where the action happens
  rather than only at render time, fails closed, and Info-logs the scope and the
  published count. Exposed through the new IRebirthCapableBrowseSession contract
  so "does this session write?" stays a type question.
- ToBrowseOptions' Last-Will landmine re-verified: MqttDriverOptions still
  carries nothing will-shaped (an NDEATH is a broker-published will and would be
  invisible to PublishCountForTest), now pinned by a reflection guard.

Falsifiability: injecting a publish into RootAsync reddens the Sparkplug and
plain passivity tests; double-publishing per target reddens all four
one-NCMD-per-node assertions. 572/572 MQTT tests, 24/24 AdminUI browsing tests.

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

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Browsing/IBrowseSession.cs

@@ -35,3 +35,47 @@ public interface IBrowseSession : IAsyncDisposable
     /// <returns>The attributes of the node.</returns>
     Task<IReadOnlyList<AttributeInfo>> AttributesAsync(string nodeId, CancellationToken cancellationToken);
 }
+
+/// <summary>
+///     An <see cref="IBrowseSession"/> whose protocol offers an explicit, operator-triggered
+///     <b>re-announce</b> action: a request that the remote peer republish its self-description so the
+///     observation window can fill without waiting for the next natural announcement. Implemented
+///     today only by the MQTT/Sparkplug browser, whose tree is built from observed NBIRTH/DBIRTH
+///     certificates.
+/// </summary>
+/// <remarks>
+///     <para>
+///         <b>This is the only interface in the browse contract that causes an outbound message.</b>
+///         Every other browse member is strictly read-only, and for the MQTT browser that read-only
+///         property is load-bearing: a picker opened by an operator runs against a live production
+///         broker. It is a separate interface, rather than an optional member on
+///         <see cref="IBrowseSession"/>, precisely so "does this session write?" stays a type
+///         question a caller cannot forget to ask.
+///     </para>
+///     <para>
+///         <b>Callers must authorize before invoking it.</b> The AdminUI routes it through
+///         <c>BrowserSessionService.RequestRebirthAsync</c>, which enforces the same
+///         <c>DriverOperator</c> policy that gates the picker's Browse affordance — an implementation
+///         cannot check that itself, since it holds no user identity.
+///     </para>
+/// </remarks>
+public interface IRebirthCapableBrowseSession : IBrowseSession
+{
+    /// <summary>
+    ///     Asks the addressed remote peer(s) to re-announce themselves.
+    /// </summary>
+    /// <param name="scope">
+    ///     The protocol-specific target. For Sparkplug: a browse <c>NodeId</c> from this session's own
+    ///     tree (group, edge node, device or metric — resolved up to the owning edge node), or a bare
+    ///     <c>{group}/{edgeNode}</c> pair for a node that has not been observed yet.
+    /// </param>
+    /// <param name="cancellationToken">Cancellation token for the operation.</param>
+    /// <returns>The number of request messages published.</returns>
+    /// <exception cref="ArgumentException"><paramref name="scope"/> is empty or unusable.</exception>
+    /// <exception cref="InvalidOperationException">
+    ///     The scope resolves to no target, or to more targets than the implementation will fan out to
+    ///     in one action. Nothing is published in either case.
+    /// </exception>
+    /// <exception cref="NotSupportedException">This session's mode has no re-announce action.</exception>
+    Task<int> RequestRebirthAsync(string scope, CancellationToken cancellationToken);
+}