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>

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Browse/IGalaxyHierarchySource.cs

@@ -0,0 +1,19 @@
+using MxGateway.Contracts.Proto.Galaxy;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Browse;
+
+/// <summary>
+///     Driver-side seam between <see cref="GalaxyDiscoverer"/> and the gateway. Production
+///     wraps <c>GalaxyRepositoryClient</c>; tests substitute a fake returning canned
+///     <see cref="GalaxyObject"/> rows so the discoverer's translation logic can be exercised
+///     without a real gRPC channel.
+/// </summary>
+public interface IGalaxyHierarchySource
+{
+    /// <summary>
+    ///     Returns the full materialised Galaxy hierarchy. The gateway client pages
+    ///     internally; this interface deliberately exposes only the post-paging shape so
+    ///     callers don't reimplement paging.
+    /// </summary>
+    Task<IReadOnlyList<GalaxyObject>> GetHierarchyAsync(CancellationToken cancellationToken);
+}