feat: remove PostHog usage telemetry entirely

Drop the once-a-day anonymous "app_opened" heartbeat to PostHog and everything
around it: telemetry.go (sendTelemetryHeartbeat, GetTelemetryEnabled/
SetTelemetryEnabled, install-ID/last-sent settings keys, PostHog host + API key)
and the startup goroutine that fired it. The 'Send anonymous usage statistics'
toggle is removed from Settings → General (TelemetryToggle + i18n keys), and the
telemetry mentions are stripped from the README and wiki.

appVersion (still used by changelog/update/livestatus/log-email) moves to a new
version.go; release.ps1 now rewrites it there instead of telemetry.go.

frontend/src/components/SettingsModal.tsx

@@ -32,7 +32,6 @@ import {
   GetDatabaseSettings, PickOpenDatabase, PickSaveDatabase, OpenDatabase, MoveDatabase, ResetDatabaseToDefault, RestartApp, CreateDatabase, RenameDatabase,
   GetMySQLSettings, SaveMySQLSettings, TestMySQLConnection, GetDBBackendStatus,
   GetAutostartPrograms, SaveAutostartPrograms, BrowseExecutable, LaunchAutostartProgram,
-  GetTelemetryEnabled, SetTelemetryEnabled,
   GetQSLDefaults, SaveQSLDefaults,
   GetExternalServices, SaveExternalServices, TestQRZUpload, TestClublogUpload, TestHRDLogUpload, TestEQSLUpload,
   GetPOTAToken, SavePOTAToken,
@@ -546,26 +545,6 @@ function AutostartPanelComponent() {
   );
 }
 
-// TelemetryToggle is a self-contained opt-out for the anonymous usage heartbeat
-// (a random install ID + version + OS, sent once a day). Real component so it
-// can own its state; embedded inside GeneralPanel.
-function TelemetryToggle() {
-  const { t } = useI18n();
-  const [on, setOn] = useState(true);
-  const [loaded, setLoaded] = useState(false);
-  useEffect(() => {
-    GetTelemetryEnabled().then((v) => setOn(!!v)).catch(() => {}).finally(() => setLoaded(true));
-  }, []);
-  return (
-    <label className="flex items-center gap-2 text-sm cursor-pointer">
-      <Checkbox checked={on} disabled={!loaded}
-        onCheckedChange={(c) => { const v = !!c; setOn(v); SetTelemetryEnabled(v).catch(() => {}); }} />
-      {t('settings.telemetry')}
-      <span className="text-xs text-muted-foreground">({t('settings.telemetryHint')})</span>
-    </label>
-  );
-}
-
 // ADIFMonitorPanel watches a list of external ADIF files (fldigi RTTY, N1MM,
 // VarAC…) and auto-imports newly appended QSOs — deliberately option-free: a
 // contact that arrives is imported and uploaded automatically like any log entry.
@@ -4694,8 +4673,6 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
             <Checkbox checked={checkUpdates} onCheckedChange={(c) => { const v = !!c; setCheckUpdates(v); writeUiPref('opslog.checkUpdates', v ? '1' : '0'); }} />
             {t('gen.checkUpdates')} <span className="text-xs text-muted-foreground">{t('gen.checkUpdatesHint')}</span>
           </label>
-          <TelemetryToggle />
-
           <MainViewPanes onChanged={onMainPaneChanged} flexAvailable={flexAvailable} icomAvailable={icomAvailable} />
 
           <div className="border-t border-border/60 pt-4 space-y-2">