Assemble an Integrant system from a loaded configuration map.

This is the half of `wagoe.system-config` that is the same in every
application: the components every Wagoe app has (database, HTTP, router,
observability, i18n), the framework modules its config switches on, and the
modules `bb scaffold generate` produced. What is left for the application is
what only it knows — see the generated `config.clj`.

Before BOU-326 this lived in the generated file, 404 lines of it, and a
second copy lived in this repository's own `src/wagoe/system_config.clj`.
Neither copy wired `:wagoe/workflow-db-schema`, so `wagoe add workflow`
produced a module whose tables were never created.

Usage:
  (system-config (config/load-config) {:extra-modules #{:wagoe/user}})

Integrant system lifecycle management for Wagoe application.

This namespace defines init-key and halt-key! multimethods for all
system components, providing proper lifecycle management and dependency
injection for the entire application.

Components:
- :wagoe/db-context - Database connection pool and adapter
- :wagoe/user-repository - User data persistence
- :wagoe/session-repository - Session data persistence
- :wagoe/user-service - User business logic orchestration
- :wagoe/logging - Structured logging and audit trails
- :wagoe/metrics - Application and business metrics collection
- :wagoe/error-reporting - Error tracking and alerting
- :wagoe/http-handler - HTTP request routing and handling
- :wagoe/http-server - Jetty HTTP server

Usage:
  (require '[wagoe.config :as config])
  (require '[wagoe.system-config :as sys-config])   ; your application's
  (require '[integrant.core :as ig])
  (def cfg (sys-config/ig-config (config/load-config)))
  (def system (ig/init cfg))
  (ig/halt! system)