feat: ESM (Enter Sends Message) for CW keyers, N1MM-style

With ESM enabled (Settings → CW Keyer), the keyer active and mode CW, Enter in
the entry strip fires a macro by QSO stage instead of logging:
- callsign field empty            → F1 (CQ)
- callsign entered (in call field) → F2 (report), then focus jumps to RST-sent
- Enter in RST-sent / RST-rcvd     → F3 (TU), which logs via its own <LOGQSO>

Works for every keyer engine (WinKeyer / serial DTR-RTS / Flex CWX / Icom CI-V)
since it routes through the shared macro sender. Enter in other fields still logs
normally, and ESM off keeps the classic Enter-to-log behaviour.

Backend: new `esm` flag on WinkeyerSettings (winkeyer.esm). Frontend: esmHandleEnter
state machine keyed off data-esm markers on the call/RST blocks, a Settings
checkbox + hint, and i18n EN/FR.

frontend/src/components/SettingsModal.tsx

@@ -1076,14 +1076,14 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
   // WinKeyer CW keyer settings + macro editor.
   type WKMac = { label: string; text: string };
   type WKSettings = {
-    enabled: boolean; engine: string; esc_clears_call: boolean;
+    enabled: boolean; engine: string; esc_clears_call: boolean; esm: boolean;
     port: string; baud: number; wpm: number; weight: number;
     lead_in_ms: number; tail_ms: number; ratio: number; farnsworth: number;
     sidetone_hz: number; mode: string; swap: boolean; autospace: boolean;
     use_ptt: boolean; serial_echo: boolean; cw_key_line: string; cw_invert: boolean; macros: WKMac[];
   };
   const [wk, setWk] = useState<WKSettings>({
-    enabled: false, engine: 'winkeyer', esc_clears_call: true,
+    enabled: false, engine: 'winkeyer', esc_clears_call: true, esm: false,
     port: '', baud: 1200, wpm: 25, weight: 50, lead_in_ms: 10,
     tail_ms: 50, ratio: 50, farnsworth: 0, sidetone_hz: 600, mode: 'iambic_b',
     swap: false, autospace: true, use_ptt: false, serial_echo: true, cw_key_line: 'dtr', cw_invert: false, macros: [],
@@ -3106,6 +3106,13 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
               <Checkbox checked={wk.esc_clears_call} onCheckedChange={(c) => setWkField({ esc_clears_call: !!c })} />
               {t('wk.escClears')}
             </label>
+            <label className="flex items-start gap-2 text-sm cursor-pointer col-span-3 pb-1.5">
+              <Checkbox checked={wk.esm} onCheckedChange={(c) => setWkField({ esm: !!c })} className="mt-0.5" />
+              <span>
+                {t('wk.esm')}
+                <span className="block text-xs text-muted-foreground">{t('wk.esmHint')}</span>
+              </span>
+            </label>
           </div>
 
           {wk.engine === 'icom' ? (