feat: add Qiniu provider support

[JackChiang233]

Summary

Added support for Qiniu AI (七牛云) as a new model provider.

What changed

• ui/web/src/constants/providers.ts - Defines Qiniu provider metadata for the web client provider list.
• ui/desktop/frontend/src/constants/providers.ts - Adds Qiniu provider constants used by the desktop frontend.
• internal/store/provider_store.go - Persists and serves Qiniu provider configuration in the backend store layer.
• internal/http/providers.go - Exposes Qiniu provider data through provider-related HTTP endpoints.
• internal/http/provider_models.go - Implements Qiniu model listing and fallback handling in provider models APIs.
• internal/http/provider_models_test.go - Verifies Qiniu provider model behavior and fallback logic with HTTP tests.
• internal/http/provider_models_catalog.go - Registers Qiniu model catalog entries used by provider model resolution.
• internal/config/config_secrets.go - Adds Qiniu secret fields to secure provider credential configuration.
• internal/config/config_load.go - Loads Qiniu provider settings from configuration sources at startup.
• internal/config/config_channels.go - Wires Qiniu provider channel mapping into config channel definitions.
• cmd/gateway_providers.go - Registers Qiniu in gateway provider bootstrap and CLI startup wiring.

Testing

go test ./...
# 70 passed 0 failed

go test ./internal/http -run Qiniu
# 1 passed 0 failed

Type

• Feature