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/condition-picker.tsx

@@ -61,7 +61,7 @@ export function ConditionPicker({
 	activeConditions,
 	onToggle,
 	onClose,
-}: ConditionPickerProps) {
+}: Readonly<ConditionPickerProps>) {
 	const ref = useRef<HTMLDivElement>(null);
 	const [flipped, setFlipped] = useState(false);
 	const [maxHeight, setMaxHeight] = useState<number | undefined>(undefined);