feat(cat): make the DTR/RTS lowering a setting

Both defaults break someone. 0.22.7 lowered the lines on Yaesu and
Kenwood and silenced a TS-990 whose interface needs RTS raised to
transmit; 0.22.8 stopped lowering them and an FT8 station reported its
output power wandering, cured by closing OpsLog — Windows raises both on
open and the interface reads one as PTT.

So it is now a checkbox on those two backends, off by default: that is
how they behaved before any of this. Xiegu keeps lowering them
unconditionally (its own report, its own explicit keying setting), and
the CI-V backend keeps the behaviour it has always had.

frontend/src/components/SettingsModal.tsx

@@ -1136,7 +1136,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
   const [modeDraft, setModeDraft] = useState('');
   const [catCfg, setCatCfg] = useState<CATSettings>({
     enabled: false, backend: 'omnirig', omnirig_rig: 1, omnirig_vfo: '', flex_host: '', flex_port: 4992, flex_spots: false, flex_decode_spots: false, flex_decode_secs: 120,
-    yaesu_port: '', yaesu_baud: 38400, kenwood_port: '', kenwood_baud: 9600, kenwood_host: '', xiegu_port: '', xiegu_baud: 19200, xiegu_addr: 0x70, xiegu_ptt_line: '',
+    yaesu_port: '', yaesu_baud: 38400, lower_lines: false, kenwood_port: '', kenwood_baud: 9600, kenwood_host: '', xiegu_port: '', xiegu_baud: 19200, xiegu_addr: 0x70, xiegu_ptt_line: '',
     icom_port: '', icom_baud: 115200, icom_addr: 0x98, icom_net_host: '', icom_net_user: '', icom_net_pass: '', icom_net_audio: false,
     tci_host: '', tci_port: 40001, tci_spots: false, poll_ms: 250, delay_ms: 0,
     digital_default: 'FT8', share_enabled: false, share_port: 4532,
@@ -2580,6 +2580,13 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
                 </Select>
                 <span className="text-xs text-muted-foreground">{t('cat.yaesuBaudHint')}</span>
               </div>
+              <div className="space-y-1">
+                <label className="flex items-center gap-2 text-xs cursor-pointer">
+                  <Checkbox checked={!!catCfg.lower_lines} onCheckedChange={(c) => setCatCfg((s) => ({ ...s, lower_lines: !!c }))} />
+                  {t('cat.lowerLines')}
+                </label>
+                <span className="text-xs text-muted-foreground">{t('cat.lowerLinesHint')}</span>
+              </div>
             </>
             )}
             {['icom', 'xiegu', 'kenwood'].includes(catCfg.backend) && (
@@ -2627,6 +2634,13 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
                 />
                 <span className="text-xs text-muted-foreground">{t('cat.kenwoodHostHint')}</span>
               </div>
+              <div className="space-y-1">
+                <label className="flex items-center gap-2 text-xs cursor-pointer">
+                  <Checkbox checked={!!catCfg.lower_lines} onCheckedChange={(c) => setCatCfg((s) => ({ ...s, lower_lines: !!c }))} />
+                  {t('cat.lowerLines')}
+                </label>
+                <span className="text-xs text-muted-foreground">{t('cat.lowerLinesHint')}</span>
+              </div>
             </>
             )}
             {catCfg.backend === 'icom' && (