92ab8f3202
What changed: X is now a dropdown showing A, B, C, AA, etc., while still saving 0, 1, 2, etc. Y is now a dropdown showing 1, 2, 3, etc., while still saving 0, 1, 2, etc. Options are limited to valid positions for the active floor and current block size. Dragging, manual dropdown changes, block resizing, and grid resizing all keep the controls synced through the existing block write/clamp path. Verification: dotnet build PlotLine.slnx passes with 0 warnings and 0 errors. No database, rendering model, transition logic, or AJAX architecture changes.