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/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientReadWriteTests.cs

@@ -0,0 +1,32 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;
+
+/// <summary>
+///     Unit tests for the IReadable/IWritable surface that don't need a live remote OPC UA
+///     server. Wire-level round-trips against a local in-process server fixture land in a
+///     follow-up PR once we have one scaffolded.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class OpcUaClientReadWriteTests
+{
+    [Fact]
+    public async Task ReadAsync_without_initialize_throws_InvalidOperationException()
+    {
+        using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-uninit");
+        await Should.ThrowAsync<InvalidOperationException>(async () =>
+            await drv.ReadAsync(["ns=2;s=Demo"], TestContext.Current.CancellationToken));
+    }
+
+    [Fact]
+    public async Task WriteAsync_without_initialize_throws_InvalidOperationException()
+    {
+        using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-uninit");
+        await Should.ThrowAsync<InvalidOperationException>(async () =>
+            await drv.WriteAsync(
+                [new WriteRequest("ns=2;s=Demo", 42)],
+                TestContext.Current.CancellationToken));
+    }
+}