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>

ItemDatabaseEditor.cs

@@ -456,9 +456,9 @@ namespace BoxPacker3D
         {
             return new NumericUpDown
             {
-                Value = (decimal)Math.Max(1, val),
                 Minimum = 1,
                 Maximum = 100000,
+                Value = (decimal)Math.Max(1, val),
                 DecimalPlaces = 0,
                 Increment = 10,
                 BackColor = Color.FromArgb(45, 45, 60),