TokenStep 0.2.8: refine Event Horizon selector icon

[Backtthefuture]

Summary

• rebuild the Event Horizon theme selector preview with a centered black hole, thin accretion disk, and gravitational-lensing arcs
• keep all artwork inside the 58 × 48 point safe area and clip glow effects to the rounded tile
• bump release defaults and current download links to 0.2.8
• add 0.2.8 release notes

Validation

• Swift unit suite: 107 tests, 0 failures
• localization and live language refresh checks
• deterministic Settings render at 1840 × 1904
• default app bundle version: 0.2.8

Scope

The main Event Horizon artwork and motion, Classic and Odyssey themes, usage accounting, quotas, leaderboard, and updater behavior are unchanged.