Two cleanups in one pass for the v1.14.0 'works on any platform' theme:
1. Response helpers — merged src/utils/responses.js and the root-level
response-helpers.js into a single module at src/utils/responses.js.
The old module had a richer set (created, noContent, validationError,
unauthorized, forbidden, notFound, conflict) and is now re-exported
from the new location. Updated 15 routes to import from
src/utils/responses and deleted the root response-helpers.js.
2. Error logger — error-handler.js now uses the unified
src/utils/logging.js#logError (same one src/app.js uses), so all errors
go to one log file with one rotation policy. Removed the dead
asyncHandler export (the real one is in src/utils/async-handler.js
and is used everywhere). Deleted the legacy error-logger.js.
Both are invisible to users — same HTTP response shapes, same log file
path, same error format. Internal-only refactor.