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/ServerCluster.cs

@@ -0,0 +1,42 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+
+/// <summary>
+///     Top-level deployment unit. 1 or 2 <see cref="ClusterNode"/> members.
+///     Per <c>config-db-schema.md</c> ServerCluster table.
+/// </summary>
+public sealed class ServerCluster
+{
+    /// <summary>Stable logical ID, e.g. "LINE3-OPCUA".</summary>
+    public required string ClusterId { get; set; }
+
+    public required string Name { get; set; }
+
+    /// <summary>UNS level 1. Canonical org value: "zb" per decision #140.</summary>
+    public required string Enterprise { get; set; }
+
+    /// <summary>UNS level 2, e.g. "warsaw-west".</summary>
+    public required string Site { get; set; }
+
+    public byte NodeCount { get; set; }
+
+    public required RedundancyMode RedundancyMode { get; set; }
+
+    public bool Enabled { get; set; } = true;
+
+    public string? Notes { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public required string CreatedBy { get; set; }
+
+    public DateTime? ModifiedAt { get; set; }
+
+    public string? ModifiedBy { get; set; }
+
+    // Navigation
+    public ICollection<ClusterNode> Nodes { get; set; } = [];
+    public ICollection<Namespace> Namespaces { get; set; } = [];
+    public ICollection<ConfigGeneration> Generations { get; set; } = [];
+}