fix(creation-draft): delete the duplicate SPEND_POOL const

CreationDraft's docstring promised it owns no rules—it delegates to NewGame.validate.
But it kept a local const POOL := 3 that mirrored NewGame.SPEND_POOL, inviting
silent disagreement if the source was changed and the copy forgotten.

Delete POOL. Use NewGame.SPEND_POOL directly in points_left(), with a comment
making it clear this is the single authority. The coupling is now enforced by
code structure, not by hope.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/scripts/ui/creation/creation_draft.gd

@@ -15,7 +15,6 @@ extends RefCounted
 ## inside construct off the same seed, immediately after MAG, and never surfaces.
 
 const NewGame = preload("res://scripts/newgame/new_game.gd")
-const POOL := 3   # mirrors NewGame.SPEND_POOL; validate() is the authority
 
 var name: String = ""
 var race_id: String = ""
@@ -65,7 +64,10 @@ func spent_total() -> int:
 
 
 func points_left() -> int:
-	return POOL - spent_total()
+	## NewGame.SPEND_POOL is the ONE authority on the pool's size. A local copy of the
+	## number would be a second thing to keep in sync, and this class's whole contract
+	## is that it keeps none.
+	return NewGame.SPEND_POOL - spent_total()
 
 
 func can_increment(stat: String) -> bool: