Use String.raw and RegExp.exec, add prefer-regexp-exec oxlint rule

Replace escaped backslash in template literal with String.raw in
auto-number.ts. Use RegExp#exec() instead of String#match() in
bestiary-adapter.ts. Enable typescript/prefer-regexp-exec in oxlint
for automated enforcement.

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

apps/web/src/adapters/bestiary-adapter.ts

@@ -170,7 +170,7 @@ function extractAc(ac: RawMonster["ac"]): {
 	}
 	if ("special" in first) {
 		// Variable AC (e.g. spell summons) — parse leading number if possible
-		const match = first.special.match(LEADING_DIGITS_REGEX);
+		const match = LEADING_DIGITS_REGEX.exec(first.special);
 		return {
 			value: match ? Number(match[1]) : 0,
 			source: first.special,