Move provider authentication status endpoints out of the legacy `/api/cli` route
namespace so auth status is exposed through the same provider module that owns
provider auth and MCP behavior.
Add `GET /api/providers/:provider/auth/status` to the provider router and route
it through the provider auth service. Remove the old `cli-auth` route file and
`/api/cli` mount now that provider auth status is handled by the unified provider
API.
Update the frontend provider auth endpoint map to call the new provider-scoped
routes and rename the endpoint constant to reflect that it is no longer CLI
specific.
- Add provider registry to manage LLM providers (Claude, Codex, Cursor, Gemini).
- Create provider routes for MCP server operations (list, upsert, delete, run).
- Implement MCP service for handling server operations and validations.
- Introduce abstract provider class and MCP provider base for shared functionality.
- Add tests for MCP server operations across different providers and scopes.
- Define shared interfaces and types for MCP functionality.
- Implement utility functions for handling JSON config files and API responses.
