fix(search): eliminate mutable regex state with matchAll

Replace manual exec loop with matchAll to eliminate cross-call mutable
lastIndex state on module-level TOKEN_PATTERN regex. matchAll clones
the regex internally, ensuring no shared state while maintaining
identical behavior and original-text offset semantics.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

src/search/tokenize.ts

@@ -38,9 +38,7 @@ export function tokenizeWithOffsets(text: string): Token[] {
     return tokens;
   }
 
-  TOKEN_PATTERN.lastIndex = 0;
+  for (const match of text.matchAll(TOKEN_PATTERN)) {
-  let match: RegExpExecArray | null;
-  while ((match = TOKEN_PATTERN.exec(text)) !== null) {
     const value = normalizeText(match[0]);
     if (value.length > 0) {
       tokens.push({ value, offset: match.index });