Add modular monolith module support

[rtcoder]

Summary

• add module contracts and a ModuleLoader for modular monolith applications
• load module services and routes during HTTP boot
• load module CLI command mappings in shift.php commands
• update route:list to include module routes only
• add Modules\ namespace autoloading
• add an example Health module with controller, service, route, and command
• remove legacy application/controller and application/routes.php entry points
• add tests for module discovery, service registration, route registration, module controller dispatch, and attribute routing via test fixtures
• document the module structure and registration flow

Validation

• composer dump-autoload
• find Engine application tests -name '*.php' -print0 | xargs -0 -n1 php -l
• composer test
• php shift.php route:list
• php shift.php health
• HTTP smoke tests:
  • GET /health -> 200 application/json
  • GET /hello -> 404 application/json

Release

• Version label added: v0.8.0