feat(data): add the drawing set client and release session

The desktop needs a cross-platform way to read and save sets and to turn
one into nests before any UI is built on it. RemoteDrawingSetStore covers
every /api/sets route with the library client's checks and conflict
handling. SetReleasePlan groups a set by material, grade, thickness, units
and cut type without I/O, so the release dialog can preview refusals
(duplicate names, drawings without material) before anything is created.

SetReleaseSession builds every group's nest through LibraryDrawingInsert
before uploading any, so a refusal leaves nothing on the server; uploads
then never cancel mid-flight, a lost reply is reconciled by the nest's
client-allocated id, and the release is posted only when every chosen
nest exists, with a same-id retry when that post fails.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Data/RemoteDrawingLibrary.cs

@@ -329,11 +329,17 @@ public sealed class RemoteDrawingLibrary : IDrawingLibraryStore, IDisposable
     }
 }
 
-/// <summary>The nest server predates the drawing library (it answered HTTP 404).</summary>
+/// <summary>The nest server predates the drawing library or another feature (it answered HTTP 404).</summary>
 public sealed class ServerTooOldException : IOException
 {
     public ServerTooOldException()
-        : base("This nest server does not support the drawing library (HTTP 404). Update the nest server to this OpenNest version.")
+        : this("the drawing library")
+    {
+    }
+
+    /// <summary><paramref name="feature"/> names what is missing, for example "drawing sets".</summary>
+    public ServerTooOldException(string feature)
+        : base($"This nest server does not support {feature} (HTTP 404). Update the nest server to this OpenNest version.")
     {
     }
 }