Improve startup performance: defer S57 chart symbols loading

## Problem `S57Service.init()` is called unconditionally in `AppFacade.parseLoadedConfig()` on every startup. This fetches and parses `chartsymbols.xml` (2.2 MB / 112 KB compressed) and `rastersymbols-day.png` (250 KB) even when no S57 vector charts are configured. ## Root cause `app.facade.ts:326`: ```ts private parseLoadedConfig() { cleanConfig(this.config, this.hostDef.params); this.doPostConfigLoad(); this.s57.init(this.config.map.s57Options); // always called } ``` The init should be deferred until an S57 chart layer is actually added to the map.