feat: reward Kata promotions by tier and recency - #1596

Summary

Updates the Autovara/kata reward configuration so Kata promotion PRs can be rewarded by both quality tier and recency.

Changes

• Adds tiered Kata reward labels:
  • kata:reward:s = 1.5x
  • kata:reward:m = 3.0x
  • kata:reward:l = 5.0x
  • kata:reward:xl = 10.0x
• Adds Kata-specific time decay:
  • 0h grace period
  • 2d sigmoid midpoint
  • 1.0 sigmoid steepness
  • 0.05 minimum multiplier
• Updates maintainer_cut from 0.4 to 0.5.
• Updates max_open_pr_threshold from 2 to 1.

Rationale

Previously, every Kata winner PR matched only kata:winner:* with a fixed 1.0x multiplier. This made weak and strong promotions indistinguishable for reward allocation.

The new tier labels allow Kata to publish a deterministic promotion-strength signal, while the time-decay config gives newer kings stronger reward weight than older winners inside the lookback window.

Validation

• Confirmed master_repositories.json remains valid JSON.