v26.2.0

• Add /gs ping so players can view their ping and compensation status.
• Add /gs toggle so players can opt their own compensation on or off.
• Make knockback compensation functional via knockback-multiplier, gated behind
  knockback.enabled (default false) so vanilla gameplay is unchanged out of the box.
• Add ping-update-interval config option to control how often ping is sampled.
• Refactor player data storage to use computeIfAbsent and drop a dead lookup.
• Remove unused knockback/velocity code paths and tidy PlayerData.