- Add `./modules/define` export path pointing to `defineModule.js`
- Implement `registerExternalModules()` to handle modules passed via `zen.config.js`, with env var gating (`ZEN_MODULE_<NAME>=true`)
- Extract `buildAdminConfig()` helper to consolidate admin navigation/page config building
- Refactor `loadModuleConfig()` to use `buildAdminConfig()` and simplify public routes check
- Improve `initializeModuleTables()` to gracefully skip modules without `db.js` instead of erroring
- Update module discovery JSDoc to reflect external module registration support
Strips out built-in clients, invoice, and nuage modules from core
handlers, module initializers, and action registries. This cleans up
hardcoded module dependencies, leaving only the posts module as a
reference implementation for the modular architecture.