feat(aura): apply ranked creeper protection

design/log.md

@@ -14,3 +14,4 @@ description: Chronological record of material changes to the Spigot Creeper Fear
 - Replaced lifetime cumulative kill tracking with a persisted rank and current-tier progress model.
 - Added the initial plugin architecture.
 - Completed US-001 with asynchronous SQLite current-tier progress, direct and indirect kill attribution, bounded death deduplication, and automated tests.
+- Completed US-002 with per-tier rank advancement, online aura state, creeper block protection, rank damage multipliers, and rank VI cancellation.

design/user-stories/us-002-unlock-creeper-aura-ranks.md

@@ -2,7 +2,7 @@
 type: User Story
 title: "US-002: Unlock Creeper Aura ranks"
 description: Protect blocks and modify creeper damage according to a player's earned aura rank.
-status: backlog
+status: done
 ---
 
 # US-002: Unlock Creeper Aura ranks
@@ -23,17 +23,17 @@ As a **player**, I want Creeper Aura to become stronger as I defeat creepers so
 
 ## Acceptance criteria
 
-- [ ] A player unlocks the next rank after earning the configured number of kills within their current tier.
-- [ ] Unlocking a rank resets current-tier progress to zero.
-- [ ] A player below rank I receives normal creeper explosion behavior.
-- [ ] An aura activates when an unlocked player would have been hit by the creeper explosion, even when armor or another modifier would reduce the eventual damage to zero.
-- [ ] An activated aura prevents that creeper explosion from breaking or removing blocks for everyone affected by the explosion.
-- [ ] Other nearby players and entities continue to receive their normal creeper explosion effects unless they have their own aura damage modifier.
-- [ ] The protected player's rank multiplier is applied to vanilla creeper explosion damage before armor, enchantments, resistance, and difficulty mitigation.
-- [ ] At rank VI, the protected player's creeper explosion damage event is cancelled so that damage and knockback are nullified.
-- [ ] Charged creepers obey the same aura rules while retaining their vanilla base explosion strength.
-- [ ] Explosions from TNT, beds, respawn anchors, and non-creeper entities are unchanged.
-- [ ] Simultaneous exposure of players with different aura ranks is deterministic and tested.
+- [x] A player unlocks the next rank after earning the configured number of kills within their current tier.
+- [x] Unlocking a rank resets current-tier progress to zero.
+- [x] A player below rank I receives normal creeper explosion behavior.
+- [x] An aura activates when an unlocked player would have been hit by the creeper explosion, even when armor or another modifier would reduce the eventual damage to zero.
+- [x] An activated aura prevents that creeper explosion from breaking or removing blocks for everyone affected by the explosion.
+- [x] Other nearby players and entities continue to receive their normal creeper explosion effects unless they have their own aura damage modifier.
+- [x] The protected player's rank multiplier is applied to vanilla creeper explosion damage before armor, enchantments, resistance, and difficulty mitigation.
+- [x] At rank VI, the protected player's creeper explosion damage event is cancelled so that damage and knockback are nullified.
+- [x] Charged creepers obey the same aura rules while retaining their vanilla base explosion strength.
+- [x] Explosions from TNT, beds, respawn anchors, and non-creeper entities are unchanged.
+- [x] Simultaneous exposure of players with different aura ranks is deterministic and tested.
 
 ## Related