Implements CorsSettings struct with validation and deserialization support
for configuring Cross-Origin Resource Sharing in the application settings.
Ref: T010 (specs/001-modbus-relay-control)
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)