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.
Restructure the provider management system by separating the monolithic
Provider model into two distinct entities:
- ProviderGroup: defines shared upstream configuration (type, base_url,
google settings, models, status)
- APIKey: represents individual credentials within a group (api_key,
weight, status, auto_ban, ban settings)
This change also updates:
- Binding model to reference GroupID instead of RouteGroup string
- All CRUD handlers for the new provider-group and api-key endpoints
- Sync service to rebuild provider snapshots from joined tables
- Model registry to aggregate capabilities across group/key pairs
- Access handler to validate namespace existence and subset constraints
- Migration importer to handle the new schema structure
- All related tests to use the new model relationships
BREAKING CHANGE: Provider API endpoints replaced with /provider-groups
and /api-keys endpoints; Binding.RouteGroup replaced with Binding.GroupID
