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>

apps/web/src/hooks/use-player-characters.ts

@@ -26,8 +26,8 @@ interface EditFields {
 	readonly name?: string;
 	readonly ac?: number;
 	readonly maxHp?: number;
-	readonly color?: string;
-	readonly icon?: string;
+	readonly color?: string | null;
+	readonly icon?: string | null;
 }
 
 export function usePlayerCharacters() {
@@ -51,7 +51,13 @@ export function usePlayerCharacters() {
 	}, []);
 
 	const createCharacter = useCallback(
-		(name: string, ac: number, maxHp: number, color: string, icon: string) => {
+		(
+			name: string,
+			ac: number,
+			maxHp: number,
+			color: string | undefined,
+			icon: string | undefined,
+		) => {
 			const id = generatePcId();
 			const result = createPlayerCharacterUseCase(
 				makeStore(),