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/Client/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests/ClientStoragePathsTests.cs

@@ -0,0 +1,48 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
+
+namespace ZB.MOM.WW.OtOpcUa.Client.Shared.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class ClientStoragePathsTests
+{
+    [Fact]
+    public void GetRoot_ReturnsCanonicalFolderName_UnderLocalAppData()
+    {
+        var root = ClientStoragePaths.GetRoot();
+        root.ShouldEndWith(ClientStoragePaths.CanonicalFolderName);
+        root.ShouldContain(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData));
+    }
+
+    [Fact]
+    public void GetPkiPath_NestsPkiUnderRoot()
+    {
+        var pki = ClientStoragePaths.GetPkiPath();
+        pki.ShouldEndWith(Path.Combine(ClientStoragePaths.CanonicalFolderName, "pki"));
+    }
+
+    [Fact]
+    public void CanonicalFolderName_IsOtOpcUaClient()
+    {
+        ClientStoragePaths.CanonicalFolderName.ShouldBe("OtOpcUaClient");
+    }
+
+    [Fact]
+    public void LegacyFolderName_IsLmxOpcUaClient()
+    {
+        // The shim depends on this specific spelling — a typo here would leak the legacy
+        // folder past the migration + break every dev-box upgrade.
+        ClientStoragePaths.LegacyFolderName.ShouldBe("LmxOpcUaClient");
+    }
+
+    [Fact]
+    public void TryRunLegacyMigration_Returns_False_On_Repeat_Invocation()
+    {
+        // Once the guard in-process has fired, subsequent calls short-circuit to false
+        // regardless of filesystem state. This is the behaviour that keeps the migration
+        // cheap on hot paths (CertificateStorePath property getter is called frequently).
+        _ = ClientStoragePaths.GetRoot(); // arms the guard
+        ClientStoragePaths.TryRunLegacyMigration().ShouldBeFalse();
+    }
+}