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/stat-block.tsx

@@ -16,10 +16,10 @@ function abilityMod(score: number): string {
 function PropertyLine({
 	label,
 	value,
-}: {
+}: Readonly<{
 	label: string;
 	value: string | undefined;
-}) {
+}>) {
 	if (!value) return null;
 	return (
 		<div className="text-sm">
@@ -34,7 +34,7 @@ function SectionDivider() {
 	);
 }
 
-export function StatBlock({ creature }: StatBlockProps) {
+export function StatBlock({ creature }: Readonly<StatBlockProps>) {
 	const abilities = [
 		{ label: "STR", score: creature.abilities.str },
 		{ label: "DEX", score: creature.abilities.dex },