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/Server/ZB.MOM.WW.OtOpcUa.Admin.Tests/RecordingHubContext.cs

@@ -0,0 +1,44 @@
+using Microsoft.AspNetCore.SignalR;
+
+namespace ZB.MOM.WW.OtOpcUa.Admin.Tests;
+
+/// <summary>
+///     Minimal in-memory <see cref="IHubContext{THub}"/> that captures SendAsync invocations for
+///     assertion. Only the methods the <c>FleetStatusPoller</c> actually calls are implemented —
+///     other interface surface throws to fail fast if the poller evolves new dependencies.
+/// </summary>
+public sealed class RecordingHubContext<THub> : IHubContext<THub> where THub : Hub
+{
+    public RecordingHubContext(RecordingHubClients clients) => Clients = clients;
+
+    public IHubClients Clients { get; }
+    public IGroupManager Groups => throw new NotImplementedException();
+}
+
+public sealed class RecordingHubClients : IHubClients
+{
+    public readonly List<RecordedMessage> SentMessages = [];
+
+    public IClientProxy All => NotUsed();
+    public IClientProxy AllExcept(IReadOnlyList<string> excludedConnectionIds) => NotUsed();
+    public IClientProxy Client(string connectionId) => NotUsed();
+    public IClientProxy Clients(IReadOnlyList<string> connectionIds) => NotUsed();
+    public IClientProxy Group(string groupName) => new RecordingClientProxy(groupName, SentMessages);
+    public IClientProxy GroupExcept(string groupName, IReadOnlyList<string> excludedConnectionIds) => NotUsed();
+    public IClientProxy Groups(IReadOnlyList<string> groupNames) => NotUsed();
+    public IClientProxy User(string userId) => NotUsed();
+    public IClientProxy Users(IReadOnlyList<string> userIds) => NotUsed();
+
+    private static IClientProxy NotUsed() => throw new NotImplementedException("not used by FleetStatusPoller");
+}
+
+public sealed class RecordingClientProxy(string target, List<RecordedMessage> sink) : IClientProxy
+{
+    public Task SendCoreAsync(string method, object?[] args, CancellationToken cancellationToken = default)
+    {
+        sink.Add(new RecordedMessage(target, method, args));
+        return Task.CompletedTask;
+    }
+}
+
+public sealed record RecordedMessage(string Target, string Method, object?[] Args);