chore(host): remove unused Database:MachineDataDb option, validation, config and docs

tests/ZB.MOM.WW.ScadaBridge.Host.Tests/StartupValidatorTests.cs

@@ -20,7 +20,6 @@ public class StartupValidatorTests
         ["ScadaBridge:Node:NodeHostname"] = "central-node1",
         ["ScadaBridge:Node:RemotingPort"] = "8081",
         ["ScadaBridge:Database:ConfigurationDb"] = "Server=localhost;Database=Config;",
-        ["ScadaBridge:Database:MachineDataDb"] = "Server=localhost;Database=MachineData;",
         ["ScadaBridge:Security:Ldap:Server"] = "ldap.example.com",
         ["ScadaBridge:Security:JwtSigningKey"] = "test-signing-key-at-least-32-chars-long",
         ["ScadaBridge:Cluster:SeedNodes:0"] = "akka.tcp://scadabridge@central-node1:8081",
@@ -303,24 +302,6 @@ public class StartupValidatorTests
         Assert.Contains("ConfigurationDb connection string required for Central", ex.Message);
     }
 
-    /// <summary>Verifies that a central node missing machine data database fails validation.</summary>
-    /// <returns>The result.</returns>
-    [Fact]
-    public void Central_MissingMachineDataDb_FailsValidation()
-    {
-        // The host requirements require MachineDataDb to be
-        // validated at startup for Central nodes, and the shipped docker appsettings
-        // (docker/central-node-a/appsettings.Central.json and central-node-b) carry
-        // the key. The earlier decision (which removed the Require) is reversed
-        // here: a missing MachineDataDb must fail fast with a clear error.
-        var values = ValidCentralConfig();
-        values.Remove("ScadaBridge:Database:MachineDataDb");
-        var config = BuildConfig(values);
-
-        var ex = Assert.Throws<InvalidOperationException>(() => StartupValidator.Validate(config));
-        Assert.Contains("MachineDataDb connection string required for Central", ex.Message);
-    }
-
     /// <summary>Verifies that a central node missing LDAP server fails validation.</summary>
     /// <returns>The result.</returns>
     [Fact]