The inner_radius/outer_radius parameters were added for multi-disk layer
support but broke the spiral effect: they introduced a gap between the
core and disk arms that made the galaxy look like detached floating disks.
Reverted to the original generation formula:
r = powf(random, 0.62) * galaxy_size
angle = arm_base + (r / galaxy_size) * twist + scatter
This sweeps systems continuously from origin to galaxy edge with density
packed near the core — arms flow naturally from the dense center outward.
Removed:
- inner_radius, outer_radius fields from DiskParams
- DISK_INNER/OUTER_RADIUS_* constants from params.rs
- 4 ParamButton variants and their handlers
- UI param rows for inner/outer radius
- randomize_disk radius logic