feat(shell): ShellState + TurnEntry HUD state model

client/scripts/ui/shell/turn_entry.gd

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+class_name TurnEntry
+extends RefCounted
+## One combatant in the turn-order rail (§2: state). Seed/placeholder now; the
+## combat turn manager (M5) becomes its writer. `side` colours the rail:
+## &"you" gold, &"ally" teal-muted, &"enemy" blood.
+
+var initials: String
+var initiative: int
+var side: StringName
+var is_active: bool
+var is_downed: bool
+
+
+func _init(p_initials: String, p_initiative: int, p_side: StringName,
+		p_is_active := false, p_is_downed := false) -> void:
+	initials = p_initials
+	initiative = p_initiative
+	side = p_side
+	is_active = p_is_active
+	is_downed = p_is_downed