iOS node distances collapse under retina density conversion

What happened

On iOS, nodes in ClientScreen appeared practically touching. NodeLayout.kt placed nodes at layout coordinates (e.g. baseDistance = 210.0). Those coordinates are later converted to Dp via position.x.toDp() in NodeItem.kt, which divides by LocalDensity.current.density. On a 3× iPhone the 210-unit gap shrinks to 70 dp — just 10 dp of air around a 60 dp node icon.

Fix

• Extracted the three iOS-specific layout distance values into internal functions (baseDistanceFor, idealDistanceFor, nodeRadiusFor in composeApp/src/commonMain/kotlin/krill/zone/app/NodeLayout.kt) so the values are testable from desktopTest without a live iOS device.
• Multiplied each iOS value by 10 (matching the factor the issue author requested):
  • baseDistance: 210 → 2100
  • idealDistance: 170 → 1700
  • nodeRadius: 40 → 400
• Added NodeLayoutIosDistanceTest in desktopTest that asserts each iOS parameter is exactly 10× its Android peer, guarding against accidental reversion.

Prevention

• Layout coordinates in NodeLayout.kt are raw floats in Compose’s “pixel” space. NodeItem.kt converts them to Dp via toDp(), which divides by the screen density. Any platform-specific layout constant must account for the density of the target device, not just the logical node count.
• When adding a new platform branch to a layout distance when block, verify the value after the toDp() round-trip: value / density.density must exceed the node’s visual diameter (CommonLayout.NODE_SIZE = 60 dp) with comfortable margin.
• Extract distance constants into internal functions (as done here) so they can be unit-tested without running on a physical device.