feat(opcua): F13b endpoint security profiles — Sign + SignAndEncrypt

OpcUaApplicationHost.BuildConfigurationAsync now populates
ServerConfiguration.SecurityPolicies + UserTokenPolicies from the new
OpcUaSecurityProfile enum on OpcUaApplicationHostOptions. Defaults expose
all three baseline profiles (None + Basic256Sha256-Sign +
Basic256Sha256-SignAndEncrypt) matching docs/security.md. UserName tokens
are SDK-encrypted with the server cert so they work on None endpoints too;
F13c will plug the LDAP validator into SessionManager.

AutoAcceptUntrustedClientCertificates surfaces as an option for dev flows;
production keeps the default (false) and operators promote rejected certs
through the Admin UI.

InternalsVisibleTo added so BuildSecurityPolicies / BuildUserTokenPolicies
stay encapsulated but unit-testable. 6 new tests cover the pure builders +
two boot-verify cases (3-profile default + hardened single-profile),
bringing the suite to 34 / 34 passing.

Closes #103. Unblocks #104 (F13c LDAP user-token validator).

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/ZB.MOM.WW.OtOpcUa.OpcUaServer.csproj

@@ -19,6 +19,10 @@
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Configuration\ZB.MOM.WW.OtOpcUa.Configuration.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests"/>
+    </ItemGroup>
+
     <ItemGroup>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
         <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>