feat(server): integrate AppState, ModuleRegistry, health check, and graceful shutdown
- Add AppState with DB, Config, EventBus, ModuleRegistry via Axum State
- ModuleRegistry now uses Arc for Clone support, builder-pattern register()
- Add /api/v1/health endpoint returning status, version, registered modules
- Add graceful shutdown on CTRL+C / SIGTERM
- erp-common utils: ID generation, timestamp helpers, code generator with tests
- Config structs now derive Clone for state sharing
- Update wiki to reflect Phase 1 completion
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