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.
- Initialize and schedule IP ban maintenance tasks in server entry point
- Perform initial IP ban sync to Redis on startup
- Implement optional JSON unmarshalling to handle null `expires_at` in API
- Add CIDR overlap validation when updating rule status to active
Implement the HTTP handler for managing global IP/CIDR bans. This
includes endpoints for creating, listing, retrieving, updating, and
deleting IP ban rules, complete with Swagger documentation and error
handling.
