Make player character color and icon optional

Clicking an already-selected color or icon in the create/edit form now
deselects it. PCs without a color use the default combatant styling;
PCs without an icon show no icon. Domain, application, persistence,
and display layers all updated to handle the optional fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/application/src/create-player-character-use-case.ts

@@ -13,8 +13,8 @@ export function createPlayerCharacterUseCase(
 	name: string,
 	ac: number,
 	maxHp: number,
-	color: string,
-	icon: string,
+	color: string | undefined,
+	icon: string | undefined,
 ): DomainEvent[] | DomainError {
 	const characters = store.getAll();
 	const result = createPlayerCharacter(