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/source-manager.tsx

@@ -8,7 +8,9 @@ interface SourceManagerProps {
 	onCacheCleared: () => void;
 }
 
-export function SourceManager({ onCacheCleared }: SourceManagerProps) {
+export function SourceManager({
+	onCacheCleared,
+}: Readonly<SourceManagerProps>) {
 	const [sources, setSources] = useState<CachedSourceInfo[]>([]);
 	const [optimisticSources, applyOptimistic] = useOptimistic(
 		sources,