feat: add upload policies, daily limits, and storage quotas

- Add environment variables to configure anonymous uploads, daily upload caps, and default user storage limits.
- Update config loader to parse and validate the new settings.
- Implement backend logic to track daily usage and active storage per user.
- Update README and `.env.example` to document the new settings and admin panels.

backend/libs/httpserver/server.go

@@ -27,8 +27,13 @@ func New(cfg config.Config, logger *slog.Logger) (*http.Server, error) {
 		uploadService.Close()
 		return nil, err
 	}
+	settingsService, err := services.NewSettingsService(uploadService.DB(), cfg.DefaultSettings)
+	if err != nil {
+		uploadService.Close()
+		return nil, err
+	}
 	stopJobs := jobs.StartAll(cfg, logger, uploadService)
-	app := handlers.NewApp(cfg, logger, renderer, uploadService, authService)
+	app := handlers.NewApp(cfg, logger, renderer, uploadService, authService, settingsService)
 
 	router := http.NewServeMux()
 	app.RegisterRoutes(router)