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>

src/config.cts

@@ -679,7 +679,6 @@ function cmdConfigSetModelProfile(cwd: string, profile: string | undefined, raw:
     error(`Usage: config-set-model-profile <${VALID_PROFILES.join('|')}>`);
   }
 
-  // eslint-disable-next-line @typescript-eslint/no-unnecessary-type-assertion
   const normalizedProfile = profile!.toLowerCase().trim();
   if (!VALID_PROFILES.includes(normalizedProfile)) {
     error(`Invalid profile '${String(profile)}'. Valid profiles: ${VALID_PROFILES.join(', ')}`);