Implement From<CorsSettings> for Cors trait to configure CORS middleware
with production-ready security validation.
- Move CorsSettings to backend/src/settings/cors.rs module
- Validate wildcard + credentials constraint (browser security policy)
- Configure allowed methods, headers, credentials, and max_age
- Add structured logging for CORS configuration
- Move tests from settings/mod.rs and startup.rs to cors module
Ref: T014
Convert project from single backend to monorepo structure with separate
frontend (Vue 3 + TypeScript + Vite) and backend directories. Updates
all configuration files and build system to support both workspaces.
Ref: T007 (specs/001-modbus-relay-control)
