fix(mqtt): close #509, #510, #512, #513, #514

Five MQTT tracker items — four AdminUI/authoring defects plus the .Browser
layering exception. No runtime driver behaviour changes.

#513 payloadFormat in a Sparkplug blob. MqttTagConfigModel.ToJson wrote the key
unconditionally. Sharper than the issue states: PayloadFormat is the one Plain
field with a NON-NULLABLE typed backing, so the write did not preserve a retyped
tag's leftover — it INVENTED "payloadFormat":"Json" in a Sparkplug tag that never
had one. Now Plain-only; preserve-unknown-keys is pinned unchanged.

#509 slashed Sparkplug metric names. The mapper already carried metricName
verbatim; only the tag Name (a RawPath segment) tripped RawPaths.ValidateSegment,
which refused the batch whole — including Node Control/Rebirth, mandatory on
every Sparkplug edge node. ToRawSegment coerces the Name and leaves the address
untouched. Coercion is not injective, so DescribeNameCollisions refuses a
colliding set BY NAME: silently merging two metrics into one tag would be worse
than the refusal it replaces. Applies to every driver, not just MQTT — the
argument is about what a Name is, not about who produced it. The sanitiser is
pinned against RawPaths.ValidateSegment rather than a copied charset.

#510 stale rebirth affordance. _canRebirth was probed once at browse-open and
sessions are reaped for idleness, so a modal left open offered an action whose
token no longer resolved. Re-probed on arm AND on confirm (the reap can land
between the two, and confirm is the one path that publishes to a live broker);
the affordance retires with an explanation instead of vanishing or erroring.

#514 rebirth on a quiet plant. The tree is birth-driven and births are never
retained, so a plant that birthed before the window opened showed an empty tree —
and the scope came only from a tree selection, so the one action that would fill
the tree could not be armed. The session already accepted a bare {group}/{edgeNode}
("the prime rebirth target"); this adds the affordance. Edge-node scope only, not
a group broadcast. The rule is extracted to SparkplugRebirthScope so it is
testable — this repo has no bUnit — and is advisory: the session re-resolves and
refuses before publishing.

#512 .Browser -> .Driver layering. TWO extractions were needed, not the one the
issue anticipated: it costed this as "the client-options builder", but the browse
session decodes births itself, so moving only that would have left the reference
exactly where it was.
  - MqttClientOptionsFactory (TLS, PEM CA-pin validator, credentials, protocol
    mapping) -> new leaf .Transport project. NOT .Contracts: that is deliberately
    transport-free and MqttClientOptions is an MQTTnet type, so .Contracts would
    hand MQTTnet to ControlPlane. This is the fix the .Browser csproj comment had
    already prescribed, against the issue's suggestion.
  - The Sparkplug protocol layer (SparkplugTopic/MessageType, SparkplugCodec,
    RebirthRequester) -> .Contracts, beside the Tahu wire schema it encodes.
Still exactly one copy of the TLS/CA-pin logic; MqttBrowserLayeringTests guards
the graph both ways.

Measured, not assumed: Driver.Mqtt.dll, Polly.Core and Serilog are now absent
from the AdminUI's output. Core.dll remains, because Driver.Sql.Browser has the
SAME violation, undocumented — the old comment blamed this browser for Core and
was wrong. Filed separately rather than fixed in passing.

Full suite green apart from the 7 known pre-existing failures (4 AbLegacy
integration, compose profiles not up; 3 Host.IntegrationTests).

Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo

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

@@ -23,12 +23,12 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser;
 ///         sanctioned publish, and it is never reached by <c>OpenAsync</c> or by any browse call.
 ///     </para>
 ///     <para>
-///         <b>Layering note.</b> Unlike every other bespoke browser here, this project references the
-///         runtime <c>.Driver</c> project (to reuse <c>MqttConnection.BuildClientOptions</c> rather
-///         than fork the TLS / CA-pin path). That is a known, deliberate exception with a documented
-///         cost and a documented clean fix — see the comment on that <c>ProjectReference</c> in
-///         <c>ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser.csproj</c> before copying this project as a
-///         template.
+///         <b>Layering note.</b> This project depends on the shared leaves only — <c>.Contracts</c> for
+///         the Sparkplug wire schema and codec, <c>.Transport</c> for
+///         <see cref="MqttClientOptionsFactory"/> — and NOT on the runtime <c>.Driver</c> project, which
+///         it used to reference under a documented exception (Gitea #512). Reuse of the TLS / CA-pin path
+///         is what that exception bought, and it is preserved: there is still exactly one copy, now in
+///         <c>.Transport</c>. Do not fork it. Pinned by <c>MqttBrowserLayeringTests</c>.
 ///     </para>
 /// </summary>
 public sealed class MqttDriverBrowser : IDriverBrowser
@@ -73,7 +73,7 @@ public sealed class MqttDriverBrowser : IDriverBrowser
 
         var filter = BuildRootFilter(opts);
         var suffix = BuildBrowseClientIdSuffix();
-        var clientOptions = MqttConnection.BuildClientOptions(ToBrowseOptions(opts), suffix, _logger);
+        var clientOptions = MqttClientOptionsFactory.BuildClientOptions(ToBrowseOptions(opts), suffix, _logger);
 
         using var openCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
         openCts.CancelAfter(OpenBudget(opts));