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

crates/erp-server/src/handlers/mod.rs

@@ -0,0 +1 @@
+pub mod health;