// Package spaserver provides a lifecycle-managed HTTP server for serving
// single-page applications (SPA) and progressive web apps (PWA) from a
// container.
//
// # Overview
//
// The server delivers static assets from a configurable directory and falls
// back to index.html for any request path that does not map to an existing
// file — the standard SPA routing contract. A health endpoint is included
// at /health with the same JSON wire format used across all Einherjar modules.
//
// # Lifecycle
//
// [NewServer] returns a [lifecycle.Component] that integrates directly with
// [launcher.New]. [Server.OnInit] builds the HTTP mux. [Server.OnStart]
// begins serving in a goroutine. [Server.OnStop] performs a graceful shutdown.
//
//	cfg := spaserver.DefaultConfig()
//	srv := spaserver.NewServer(logger, cfg)
//
//	lc := launcher.New(logger)
//	lc.Append(srv)
//	if err := lc.Run(); err != nil {
//	    log.Fatal(err)
//	}
//
// # Configuration
//
// All fields are read from environment variables:
//
//   - EINHERJAR_SPA_PORT       — listen port (default: 8080)
//   - EINHERJAR_SPA_STATIC_DIR — path to the directory containing index.html and assets (default: /srv/www)
//   - EINHERJAR_LOG_LEVEL      — log level: DEBUG, INFO, WARN, ERROR (default: INFO)
//
// # Container usage
//
// The module ships as a ready-to-use base image. A downstream SPA Dockerfile
// only needs to copy the built assets:
//
//	FROM code.nochebuena.dev/einherjar/spa-server:v1.0.0
//	COPY dist/ /srv/www/
package spaserver