feat(progression): lower default rank I threshold

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

@@ -13,7 +13,7 @@ As a **player**, I want Creeper Aura to become stronger as I defeat creepers so
 
 | Current state | Kills needed to unlock next rank | Damage to protected player | Creeper block damage |
 | --- | ---: | ---: | --- |
-| Locked | 100 to unlock I | 1× | Normal |
+| Locked | 25 to unlock I | 1× | Normal |
 | Creeper Aura I | 100 to unlock II | 3× | Prevented |
 | Creeper Aura II | 100 to unlock III | 2× | Prevented |
 | Creeper Aura III | 100 to unlock IV | 1.5× | Prevented |
@@ -23,7 +23,7 @@ As a **player**, I want Creeper Aura to become stronger as I defeat creepers so
 
 ## Acceptance criteria
 
-- [x] A player unlocks the next rank after earning the configured number of kills within their current tier.
+- [x] A player unlocks rank I after 25 kills by default; subsequent ranks require 100 kills each by default.
 - [x] Unlocking a rank resets current-tier progress to zero.
 - [x] A player below rank I receives normal creeper explosion behavior.
 - [x] An aura protects blocks when a player with rank I or higher is within 25 blocks of a creeper at explosion time, including at exactly 25 blocks.

design/user-stories/us-006-configure-aura-progression.md

@@ -11,7 +11,7 @@ As a **server administrator**, I want to configure progression and aura behavior
 
 ## Acceptance criteria
 
-- [x] Configuration provides documented defaults for the six per-rank kill requirements and six unlocked-rank damage multipliers.
+- [x] Configuration defaults to 25 kills for rank I, 100 kills for each subsequent rank, and the documented six unlocked-rank damage multipliers.
 - [x] Rank requirements are positive integers.
 - [x] Damage multipliers are finite and non-negative.
 - [x] Progress boss-bar duration and player-facing rank messages are configurable.