chore: clean up clear-cut ESLint warnings (#732) (#734)

Pay down pre-existing error→warn lint debt. Removes dead imports/vars, unused functions, redundant regex/string escapes, and stale eslint-disable directives; converts unused `catch (_e)` to optional catch binding (src/*.cts).

No behavior change. Lint 345→125 warnings (0 errors); deferred categories (n/no-process-exit, test-sleeps, control-regex) tracked in #732 for follow-up. Full test suite green (0 failures); code-review verified all removals unused and all escape fixes semantics-preserving.

Closes #732

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

scripts/sync-runtime-launcher.cjs

@@ -96,9 +96,6 @@ function removeResolverLines(lines, preamble) {
   const result = [];
   let i = 0;
 
-  // Build a set of preamble lines for fast lookup (to strip previously-inserted preambles)
-  const preambleLineSet = new Set(preamble);
-
   while (i < lines.length) {
     const line = lines[i];
     const trimmed = line.trim();