feat(accounts): implement user accounts, sessions, and dashboards

Introduce Stage 4 features to support multi-user accounts, cookie-based web sessions, and personal dashboards.

Changes include:
- Adding `/register` to bootstrap the first admin account and `/login`/`/logout` for session management.
- Creating a personal dashboard (`/app`) to display owned boxes, storage usage, and upload history.
- Implementing admin user management (`/admin/users`) for generating invite links and managing user states.
- Updating the bbolt database schema to store users, sessions, invites, and collections.
- Adding `golang.org/x/crypto` for password hashing and introducing unit tests for account handlers.

backend/libs/httpserver/server.go

@@ -22,8 +22,13 @@ func New(cfg config.Config, logger *slog.Logger) (*http.Server, error) {
 	if err != nil {
 		return nil, err
 	}
+	authService, err := services.NewAuthService(uploadService.DB(), cfg.BaseURL)
+	if err != nil {
+		uploadService.Close()
+		return nil, err
+	}
 	stopJobs := jobs.StartAll(cfg, logger, uploadService)
-	app := handlers.NewApp(cfg, logger, renderer, uploadService)
+	app := handlers.NewApp(cfg, logger, renderer, uploadService, authService)
 
 	router := http.NewServeMux()
 	app.RegisterRoutes(router)