- SpikeParameters: added GrooveDepth (how deep groove cuts into
receiving part) and SpikeWeldGap (gap between spike tip and groove)
- SpikeGrooveSplit: groove uses its own depth (wider/deeper than spike),
spike tip stops short by weld gap amount
- UI: added Groove Depth and Weld Gap fields to spike parameters panel
- Changed default pair count to 2 (one near each end)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
