feat(newgame): the seeded creation pipeline

construct() takes a seed, not a stat block. It rebuilds the RNG and rolls the
attributes itself, so it never trusts a number handed to it (§2) and the same seed
yields an identical character, hidden Luck included (§10). The whole character is
reproducible from four primitives: seed, race_id, calling_id, spend. The rng
parameter is dropped — the seed is now the only source of randomness.

The roll is 3d6 with a hard floor of 8. Straight 3d6 puts ~9% on a primary the +3
pool cannot rescue, and a character bad at the one thing he is FOR is not grit —
it is the fine §7 forbids, paid for twenty hours.

LCK is unspendable, not merely hidden: spending on it is a validation error.
GameState.stats becomes GameState.sheet.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QYa9u7Kdxv5gX4AnwWexy8

client/scripts/state/game_state.gd

@@ -6,7 +6,7 @@ extends RefCounted
 
 var luck: int = 0
 var luck_base: int = 0
-var stats: Dictionary = {}            # {str, dex, con, fth, mag}
+var sheet: CharacterSheet = null       # the whole character (§2). Built by NewGame.
 var npc_dispositions: Dictionary = {} # world-npc id -> int (−100..100)
 var inventory: Dictionary = {}        # item_id -> qty (NEVER money — see purse_copper)
 var purse_copper: int = 0             # ALL money, in copper. One integer (§4.1 of the spec).