feat: Help - What's new button to reopen the changelog anytime

Adds GetChangelog (all entries up to the running version, no seen-marker change)
and a Help menu 'What's new' item that reopens the changelog dialog on demand.

frontend/src/App.tsx

@@ -13,7 +13,7 @@ import {
   GetQSO, UpdateQSO, DeleteQSO, DeleteQSOs, DeleteAllQSO,
   UpdateQSOsFromCty, UpdateQSOsFromQRZ, UpdateQSOsFromClublog, UploadQSOsManual, SendQSORecordingEmail,
   LookupCallsign, GetStationSettings, GetListsSettings,
-  GetStartupStatus, CheckForUpdate, DownloadAndApplyUpdate, GetLiveStations, GetWhatsNew,
+  GetStartupStatus, CheckForUpdate, DownloadAndApplyUpdate, GetLiveStations, GetWhatsNew, GetChangelog,
   WorkedBefore,
   SetCompactMode,
   GetCATState, SetCATFrequency, SetCATMode, SwitchCATRig, FlexApplyBandAntenna,
@@ -2801,6 +2801,7 @@ export default function App() {
       { type: 'item', label: refsDownloading ? 'Downloading reference lists…' : 'Download reference lists (IOTA/POTA/WWFF/SOTA)', action: 'tools.downloadRefs', disabled: refsDownloading },
     ]},
     { name: 'help', label: t('menu.help'), items: [
+      { type: 'item', label: t('whatsnew.title'), action: 'help.whatsnew' },
       { type: 'item', label: t('help.about'), action: 'help.about' },
     ]},
   ], [total, selectedId, selectedIds, ctyRefreshing, refsDownloading, exporting, wkEnabled, dvkEnabled, netEnabled, contestTabEnabled, t]);
@@ -2831,6 +2832,7 @@ export default function App() {
       case 'tools.refreshCty':  refreshCtyDat(); break;
       case 'tools.downloadRefs': downloadRefs(); break;
       case 'help.about':        setShowAbout(true); break;
+      case 'help.whatsnew':     GetChangelog().then((e: any) => { if (Array.isArray(e) && e.length) setWhatsNew(e); else showToast(t('whatsnew.none')); }).catch(() => {}); break;
     }
   }