feat: Themes added, 4 themes available (3 dark, 1 light)

frontend/src/lib/uiPref.ts

@@ -10,6 +10,7 @@ import { GetUIPref, SetUIPref } from '../../wailsjs/go/main/App';
 // Keys that must travel with data/ (DB is the portable source of truth; the
 // localStorage copy is just a fast, synchronous cache).
 const PORTABLE_KEYS = [
+  'opslog.theme',         // UI colour theme (light-warm / dark-warm / graphite / high-contrast / auto)
   'hamlog.qsoLimit',      // QSO list page size
   'bandmap.side',         // band map docked left / right
   'bandmap.show',         // band map open / closed