Add shared response DTOs and enhance the response envelope middleware with
excluded paths, trace ID generation fallback, and automatic extraction of
error details from handler responses. Update default business code mapping
for 503 and 504, and adjust idempotency detection to only treat the new
envelope format as already-wrapped.
BREAKING CHANGE: responses using the old envelope format (e.g., string
`code`) are now wrapped into the new standard envelope.
Add numeric business codes, include `trace_id`, and support custom
error messages and `details` for error responses while keeping envelope
wrapping idempotent across old and new formats.
BREAKING CHANGE: response envelope `code` changes from string to int and
envelope format now includes `trace_id` (and may include `details`).
Add response envelope middleware to standardize JSON responses as
`{code,data,message}` with consistent business codes across endpoints.
Update Swagger annotations and tests to reflect the new response shape.
BREAKING CHANGE: API responses are now wrapped in a response envelope; clients must read payloads from `data` and handle `code`/`message` fields.
