Rewrite LayerPacker as skyline packer, add Extreme Points alternative, manual footprint tuning and reordering UI

- Replace the old layer-grid LayerPacker with a skyline (lowest-slot-first) algorithm:
  grows the footprint only when items truly can't fit within maxBox, lets shorter
  types stack multiple sub-layers into taller leftover space, cascades unfinished
  layers to later types, and allows a staircase profile to minimize wasted volume.
- Fix ItemDatabaseEditor NumericUpDown crash (Value set before Minimum/Maximum) and
  ItemDatabase.Upsert doing INSERT instead of UPDATE (was keyed by Name, now by Id).
- Add Packer3D as a working Extreme Points algorithm (was dead/commented-out code)
  behind a shared IPacker interface, selectable in the UI alongside Skyline.
- Add manual footprint (Skyline) / box-size (Extreme Points) adjustment controls for
  the first box, with correct min/max clamping against the configured max box size.
- Add a "Poradie" column with up/down buttons to reorder packing items; both packers
  now honor that manual order instead of re-sorting by volume.
- Drop multi-box packing (single box only), add a pre-pack volume warning, and make
  unpacked items exportable to PDF / inspectable via a result-label tooltip, both
  grouped by type with dimensions, count and total volume.
- Merge the min/max box dimension groups, hide the now-unused box navigation group,
  and misc UI cleanup (typo fix, group renames, wider item name column).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

ItemDatabase.cs

@@ -107,18 +107,29 @@ namespace BoxPacker3D
             return null;
         }
 
-        /// <summary>Inserts or replaces a template (upsert by Name).</summary>
+        /// <summary>
+        /// Inserts a new template (Id == 0) or updates the existing row by Id (Id &gt; 0).
+        /// Using Id rather than Name for the update key means renaming an existing item
+        /// during edit correctly updates that same row instead of leaving the old-named
+        /// row behind and inserting a new one.
+        /// </summary>
         public void Upsert(ItemTemplate item)
         {
             using var conn = Open();
             using var cmd = conn.CreateCommand();
-            cmd.CommandText = @"
-                INSERT INTO items (Name, Width, Height, Depth)
-                VALUES ($n, $w, $h, $d)
-                ON CONFLICT(Name) DO UPDATE SET
-                    Width = excluded.Width,
-                    Height = excluded.Height,
-                    Depth = excluded.Depth;";
+            if (item.Id > 0)
+            {
+                cmd.CommandText = @"
+                    UPDATE items SET Name = $n, Width = $w, Height = $h, Depth = $d
+                    WHERE Id = $id;";
+                cmd.Parameters.AddWithValue("$id", item.Id);
+            }
+            else
+            {
+                cmd.CommandText = @"
+                    INSERT INTO items (Name, Width, Height, Depth)
+                    VALUES ($n, $w, $h, $d);";
+            }
             cmd.Parameters.AddWithValue("$n", item.Name);
             cmd.Parameters.AddWithValue("$w", item.Width);
             cmd.Parameters.AddWithValue("$h", item.Height);