feat(abcip): final review I1 — node-level Drivers:AbCip:DefaultTransport

The old AdminUI cannot author the per-driver transport key (#576), so the
'pin before upgrading' recipe had no working path. A node-level appsetting
(env Drivers__AbCip__DefaultTransport) now supplies the default for AbCip
drivers with no key: explicit key > node default > compiled Native. Bound
and validated unconditionally (bad value fails host start); the driver
factory and the Test Connect probe both read it so they agree. AbCip.md
upgrade recipe rewritten around the key; Configuration.md documents it.
Also documents first-wins for AllowPacking/probe and host-alias throttles
(final review M6) and moves the status-bit note out of AbCip.md (M5).

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

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

@@ -35,11 +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="">Default (Native)</option>
+                    <option value="">Default (node setting; Native unless pinned)</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. Default omits the setting so the driver picks; takes effect on the next deploy.</div>
+                <div class="form-text">Which protocol stack talks to the controller. Default omits the setting so the node-level <code>Drivers:AbCip:DefaultTransport</code> picks (Native unless an operator pinned it); takes effect on the next deploy.</div>
             </div>
         </div>
     </div>