test(fixtures): migrate integration-test fixture defaults to 10.100.0.35

CLAUDE.md "Docker Workflow" claims (per the 2026-04-28 migration note)
that all fixture-class default endpoints were rewritten to target the
shared Docker host at 10.100.0.35. Audit during today's e2e run showed
the claim was incomplete — five fixture classes still defaulted to
localhost / 127.0.0.1, causing every fixture-touching integration test
to skip with "endpoint unreachable" on a fresh box that hadn't set
the override env vars.

Files corrected:

  - tests/.../Modbus.IntegrationTests/ModbusSimulatorFixture.cs
      DefaultEndpoint: localhost:5020 → 10.100.0.35:5020
  - tests/.../S7.IntegrationTests/Snap7ServerFixture.cs
      DefaultEndpoint: localhost:1102 → 10.100.0.35:1102
  - tests/.../OpcUaClient.IntegrationTests/OpcPlcFixture.cs
      DefaultEndpoint: opc.tcp://localhost:50000 → opc.tcp://10.100.0.35:50000
  - tests/.../AbCip.IntegrationTests/AbServerFixture.cs
      Host default + ResolveHost fallback: 127.0.0.1 → 10.100.0.35
  - tests/.../AbLegacy.IntegrationTests/AbLegacyServerFixture.cs
      Host default + ResolveEndpoint fallback: 127.0.0.1 → 10.100.0.35

XML doc comments referencing the old localhost defaults were updated in
the same pass so the class-summary documentation matches the actual
default. The override-via-env-var mechanism (MODBUS_SIM_ENDPOINT,
AB_SERVER_ENDPOINT, AB_LEGACY_ENDPOINT, S7_SIM_ENDPOINT,
OPCUA_SIM_ENDPOINT) is unchanged — pointing at a real PLC or a
locally-running container still works exactly as before.

Verification:
  - Solution-wide dotnet build: 0 errors.
  - S7.IntegrationTests: 3/3 pass without env-var override.
  - OpcUaClient.IntegrationTests: 3/3 pass without env-var override.
  - Modbus.IntegrationTests: 4/38 (same as the env-var-override run —
    the 2 failures + 32 skips are pre-existing fixture-profile
    mismatches unrelated to this fix).
  - AbCip.IntegrationTests / AbLegacy.IntegrationTests: same results
    as the env-var-override run.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/ModbusSimulatorFixture.cs

@@ -5,7 +5,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests;
 /// <summary>
 ///     Reachability probe for a Modbus TCP simulator (pymodbus in Docker, see
 ///     <c>Docker/docker-compose.yml</c>) or a real PLC. Parses
-///     <c>MODBUS_SIM_ENDPOINT</c> (default <c>localhost:5020</c> per PR 43) and TCP-connects once at
+///     <c>MODBUS_SIM_ENDPOINT</c> (default <c>10.100.0.35:5020</c> — the shared Docker host) and TCP-connects once at
 ///     fixture construction. Each test checks <see cref="SkipReason"/> and calls
 ///     <c>Assert.Skip</c> when the endpoint was unreachable, so a dev box without a running
 ///     simulator still passes `dotnet test` cleanly — matches the Galaxy live-smoke pattern in
@@ -29,8 +29,11 @@ public sealed class ModbusSimulatorFixture : IAsyncDisposable
     // PR 43: default port is 5020 (pymodbus convention) instead of 502 (Modbus standard).
     // Picking 5020 sidesteps the privileged-port admin requirement on Windows + matches the
     // port baked into the pymodbus simulator JSON profiles in Docker/profiles/. Override with
-    // MODBUS_SIM_ENDPOINT to point at a real PLC on its native port 502.
-    private const string DefaultEndpoint = "localhost:5020";
+    // MODBUS_SIM_ENDPOINT to point at a real PLC on its native port 502, or to a
+    // locally-running container if the shared host is unavailable.
+    // 10.100.0.35 = the shared Docker host (see CLAUDE.md "Docker Workflow"). Migrated
+    // off this VM's localhost on 2026-04-28 alongside the rest of the Docker-host move.
+    private const string DefaultEndpoint = "10.100.0.35:5020";
     private const string EndpointEnvVar = "MODBUS_SIM_ENDPOINT";
 
     public string Host { get; }