chore: organize solution into module folders (Core/Server/Drivers/Client/Tooling)

Group all 69 projects into category subfolders under src/ and tests/ so the
Rider Solution Explorer mirrors the module structure. Folders: Core, Server,
Drivers (with a nested Driver CLIs subfolder), Client, Tooling.

- Move every project folder on disk with git mv (history preserved as renames).
- Recompute relative paths in 57 .csproj files: cross-category ProjectReferences,
  the lib/ HintPath+None refs in Driver.Historian.Wonderware, and the external
  mxaccessgw refs in Driver.Galaxy and its test project.
- Rebuild ZB.MOM.WW.OtOpcUa.slnx with nested solution folders.
- Re-prefix project paths in functional scripts (e2e, compliance, smoke SQL,
  integration, install).

Build green (0 errors); unit tests pass. Docs left for a separate pass.

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

tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/InterfaceIndependenceTests.cs

@@ -0,0 +1,71 @@
+using System.Reflection;
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests;
+
+/// <summary>
+///     Asserts that <c>Core.Abstractions</c> stays a true contract project — it must not depend on
+///     any implementation type, any other OtOpcUa project, or anything beyond BCL + System types.
+///     Per <c>docs/v2/plan.md</c> decision #59 (Core.Abstractions internal-only for now; design as
+///     if public to minimize churn later).
+/// </summary>
+public sealed class InterfaceIndependenceTests
+{
+    private static readonly Assembly Assembly = typeof(IDriver).Assembly;
+
+    [Fact]
+    public void Assembly_HasNoReferencesOutsideBcl()
+    {
+        // Allowed reference assembly name prefixes — BCL + the assembly itself.
+        var allowed = new[]
+        {
+            "System",
+            "Microsoft.Win32",
+            "netstandard",
+            "mscorlib",
+            "ZB.MOM.WW.OtOpcUa.Core.Abstractions",
+        };
+
+        var referenced = Assembly.GetReferencedAssemblies();
+        var disallowed = referenced
+            .Where(r => !allowed.Any(a => r.Name!.StartsWith(a, StringComparison.Ordinal)))
+            .ToList();
+
+        disallowed.ShouldBeEmpty(
+            $"Core.Abstractions must reference only BCL/System assemblies. " +
+            $"Found disallowed references: {string.Join(", ", disallowed.Select(a => a.Name))}");
+    }
+
+    [Fact]
+    public void AllPublicTypes_LiveInRootNamespace()
+    {
+        // Per the decision-#59 "design as if public" rule — no nested sub-namespaces; one flat surface.
+        var publicTypes = Assembly.GetExportedTypes();
+        var nonRoot = publicTypes
+            .Where(t => t.Namespace != "ZB.MOM.WW.OtOpcUa.Core.Abstractions")
+            .ToList();
+
+        nonRoot.ShouldBeEmpty(
+            $"Core.Abstractions should expose all public types in the root namespace. " +
+            $"Found types in other namespaces: {string.Join(", ", nonRoot.Select(t => $"{t.FullName}"))}");
+    }
+
+    [Theory]
+    [InlineData(typeof(IDriver))]
+    [InlineData(typeof(ITagDiscovery))]
+    [InlineData(typeof(IReadable))]
+    [InlineData(typeof(IWritable))]
+    [InlineData(typeof(ISubscribable))]
+    [InlineData(typeof(IAlarmSource))]
+    [InlineData(typeof(IHistoryProvider))]
+    [InlineData(typeof(IRediscoverable))]
+    [InlineData(typeof(IHostConnectivityProbe))]
+    [InlineData(typeof(IDriverConfigEditor))]
+    [InlineData(typeof(IAddressSpaceBuilder))]
+    public void EveryCapabilityInterface_IsPublic(Type type)
+    {
+        type.IsPublic.ShouldBeTrue($"{type.Name} must be public — drivers in separate assemblies implement it.");
+        type.IsInterface.ShouldBeTrue($"{type.Name} must be an interface, not a class.");
+    }
+}