fix(utils): findAndReplace infinite loop on non-global regex + tests (+28)

Prevention work surfaced a real latent bug: findAndReplace looped forever
(OOM) on any non-global regex with a match — `match` was only reassigned
inside `if (regex.global)`, so a non-global regex never advanced. Fixed by
treating a non-global regex as a single match (`match = regex.global ?
regex.exec(text) : null`) and added a regression test. Latent in practice
(all current callers pass global regexes), but a crash waiting to happen.

New suites (tsx + node:test), verified empirically:
- utils/findAndReplace (10, incl. the regression)
- utils/AsyncSearch (9): normalize + matchQuery (the timer-based class is
  skipped — needs window.performance/setTimeout, unavailable in node)
- utils/ASCIILexicalTable (10): orderKeys gap-filling + invariants

Full suite now 103 tests, all passing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/utils/findAndReplace.ts

@@ -19,7 +19,10 @@ export const findAndReplace = <ReplaceReturnType, ConvertReturnType>(
     result.push(replace(match, result.length));
 
     lastEnd = match.index + match[0].length;
-    if (regex.global) match = regex.exec(text);
+    // A non-global regex always returns the same first match from exec() (its
+    // lastIndex never advances), so re-running it would loop forever. Treat a
+    // non-global regex as a single match and stop after processing it.
+    match = regex.global ? regex.exec(text) : null;
   }
 
   result.push(convertPart(text.slice(lastEnd), result.length));