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>

tests/hardcoded-paths.test.cjs

@@ -55,7 +55,7 @@ const sourceFiles = sourceDirs.flatMap(collectSourceFiles);
  * Scan files for a pattern, skipping comment lines.
  * Returns an array of human-readable failure strings.
  */
-function scanFiles(files, pattern, description) {
+function scanFiles(files, pattern, _description) {
   const failures = [];
   for (const file of files) {
     const content = fs.readFileSync(file, 'utf8');