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/Core/ZB.MOM.WW.OtOpcUa.Configuration/Entities/UnsArea.cs

@@ -0,0 +1,21 @@
+namespace ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+
+/// <summary>UNS level-3 segment. Generation-versioned per decision #115.</summary>
+public sealed class UnsArea
+{
+    public Guid UnsAreaRowId { get; set; }
+
+    public long GenerationId { get; set; }
+
+    public required string UnsAreaId { get; set; }
+
+    public required string ClusterId { get; set; }
+
+    /// <summary>UNS level 3 segment: matches <c>^[a-z0-9-]{1,32}$</c> OR equals literal <c>_default</c>.</summary>
+    public required string Name { get; set; }
+
+    public string? Notes { get; set; }
+
+    public ConfigGeneration? Generation { get; set; }
+    public ServerCluster? Cluster { get; set; }
+}