- Replace raw Panel with EntityView (via SplitPreview subclass) for proper
zoom-to-point, middle-button pan, and double-buffered rendering
- Add draggable handles for tab/spike positions along split lines; positions
flow through to WeldGapTabSplit and SpikeGrooveSplit via SplitLine.FeaturePositions
- Fix OK/Cancel buttons hidden off-screen by putting them in a bottom-docked panel
- Fix DrawControl not invalidating on resize
- Swap plate Width/Length label order, default edge spacing to 0.5
- Rename tab labels: Tab Width→Tab Length, Tab Height→Weld Gap, default count 2
- Spike depth now calculated (read-only), groove depth means positioning depth
beyond spike tip (default 0.125), converted to total depth internally
- Set entity layers visible so EntityView renders them
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>