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/ExternalIdReservation.cs

@@ -0,0 +1,36 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+
+/// <summary>
+///     Fleet-wide rollback-safe reservation of ZTag and SAPID. Per decision #124 — NOT generation-versioned.
+///     Exists outside generation flow specifically because old generations and disabled equipment can
+///     still hold the same external IDs; per-generation uniqueness indexes fail under rollback/re-enable.
+/// </summary>
+public sealed class ExternalIdReservation
+{
+    public Guid ReservationId { get; set; }
+
+    public required ReservationKind Kind { get; set; }
+
+    public required string Value { get; set; }
+
+    /// <summary>The equipment that owns this reservation. Stays bound even when equipment is disabled.</summary>
+    public Guid EquipmentUuid { get; set; }
+
+    /// <summary>First cluster to publish this reservation.</summary>
+    public required string ClusterId { get; set; }
+
+    public DateTime FirstPublishedAt { get; set; } = DateTime.UtcNow;
+
+    public required string FirstPublishedBy { get; set; }
+
+    public DateTime LastPublishedAt { get; set; } = DateTime.UtcNow;
+
+    /// <summary>Non-null when explicitly released by FleetAdmin (audit-logged, requires reason).</summary>
+    public DateTime? ReleasedAt { get; set; }
+
+    public string? ReleasedBy { get; set; }
+
+    public string? ReleaseReason { get; set; }
+}