feat(ab): native managed transport is the default for AbCip and AbLegacy; libplctag remains as fallback

Task 22 (spec section 8 P5), with the controller rulings that exclude PLC-5 and LogixPccc.

- Transport is nullable on both option records; null (key absent) means "use the default" and is
  never serialized. Factory DTO parse: absent -> null; a bad value still fails via ParseEnum.
- One resolver per driver (AbCipTransportResolver / AbLegacyTransportResolver), used by the driver
  constructor, the Test Connect probe and (through the driver) the CLI.
  AbCip: null -> Native. AbLegacy: null -> Native unless any device is Plc5 or LogixPccc, then the
  whole driver resolves to Libplctag. Explicit values always win; explicit Native with a
  Plc5/LogixPccc device logs one Warning at init.
- Init log shows configured vs effective, e.g. transport=Native (default).
- AdminUI forms: "Default (...)" / "Native (managed)" / "libplctag (fallback)". Default omits the
  key on save (reverses Task 19's explicit re-emit, which would have pinned every edited driver).
- CLIs: --transport default|native|libplctag, default "default" via the resolver, so
  --plc-type Plc5 with no --transport runs libplctag.
- Tests pinned to Libplctag where a default-path runtime was created: found by instrumenting the
  native factories with the current xUnit test name (one unit test, AbLegacyReinitConfigAdoption;
  plus the two fixture-gated AbCip probe E2E tests whose exact messages were proven on libplctag).
  TransportMatrix and the differential harness already pass explicit transports.
- Switch/resolver/CLI/form tests are falsified by mutating the resolver (default -> Libplctag,
  exclusion removed, AbLegacy default -> Libplctag): each mutation turns them red.
- Replaces the inline role-name literal in AbCipDriverFactoryExtensions' ParseEnum call with a named
  constant; RoleAuthorityGuardTests was already red on the base commit for that line.
- Docs: AbCip.md / AbLegacy.md default + release note; CLAUDE.md AB section.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Forms/AbCipDriverForm.razor

@@ -35,10 +35,11 @@
             <div class="col-md-3">
                 <label class="form-label" for="abcipTransport">Transport</label>
                 <InputSelect @bind-Value="_form.Transport" @bind-Value:after="EmitAsync" class="form-select form-select-sm" id="abcipTransport">
-                    <option value="@AbCipTransport.Libplctag">libplctag (default)</option>
+                    <option value="">Default (Native)</option>
                     <option value="@AbCipTransport.Native">Native (managed)</option>
+                    <option value="@AbCipTransport.Libplctag">libplctag (fallback)</option>
                 </InputSelect>
-                <div class="form-text">Which protocol stack talks to the controller. Takes effect on the next deploy.</div>
+                <div class="form-text">Which protocol stack talks to the controller. Default omits the setting so the driver picks; takes effect on the next deploy.</div>
             </div>
         </div>
     </div>
@@ -175,7 +176,10 @@
     {
         // Operation
         public int TimeoutSeconds { get; set; } = 2;
-        public AbCipTransport Transport { get; set; } = AbCipTransport.Libplctag;
+        // Null = "Default": the transport key is OMITTED on save so the driver resolves it (and the AbLegacy
+        // PLC-5 / LogixPccc exclusion still applies). Never re-emit a concrete default here — that would pin
+        // every edited driver to it.
+        public AbCipTransport? Transport { get; set; }
         public bool EnableControllerBrowse { get; set; } = false;
         public bool EnableDeclarationOnlyUdtGrouping { get; set; } = false;
 

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Forms/AbLegacyDriverForm.razor

@@ -22,10 +22,11 @@
             <div class="col-md-3">
                 <label class="form-label" for="ablegacyTransport">Transport</label>
                 <InputSelect @bind-Value="_form.Transport" @bind-Value:after="EmitAsync" class="form-select form-select-sm" id="ablegacyTransport">
-                    <option value="@AbLegacyTransport.Libplctag">libplctag (default)</option>
+                    <option value="">Default (Native; libplctag for PLC-5 / LogixPccc)</option>
                     <option value="@AbLegacyTransport.Native">Native (managed)</option>
+                    <option value="@AbLegacyTransport.Libplctag">libplctag (fallback)</option>
                 </InputSelect>
-                <div class="form-text">Which protocol stack talks to the controller. Takes effect on the next deploy.</div>
+                <div class="form-text">Which protocol stack talks to the controller. Default omits the setting so the driver picks; takes effect on the next deploy.</div>
             </div>
         </div>
     </div>
@@ -140,7 +141,10 @@
     {
         // Operation
         public int TimeoutSeconds { get; set; } = 2;
-        public AbLegacyTransport Transport { get; set; } = AbLegacyTransport.Libplctag;
+        // Null = "Default": the transport key is OMITTED on save so the driver resolves it (and the AbLegacy
+        // PLC-5 / LogixPccc exclusion still applies). Never re-emit a concrete default here — that would pin
+        // every edited driver to it.
+        public AbLegacyTransport? Transport { get; set; }
 
         // Probe
         public bool ProbeEnabled { get; set; } = true;