Use Readonly props and optional chaining/nullish coalescing

Mark component props as Readonly<> across 15 component files and
simplify edit-player-character field access with optional chaining
and nullish coalescing.

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

apps/web/src/components/player-management.tsx

@@ -21,7 +21,7 @@ export function PlayerManagement({
 	onEdit,
 	onDelete,
 	onCreate,
-}: PlayerManagementProps) {
+}: Readonly<PlayerManagementProps>) {
 	useEffect(() => {
 		if (!open) return;
 		function handleKeyDown(e: KeyboardEvent) {