feat: record a contact by hand when automatic recording is off

A red dot in the slot the counter will occupy. Click it and the counter starts,
the dot disappears, and logging the QSO writes the file exactly as an automatic
recording would — the save path already keyed off an active take, not off the
setting.

With automatic recording disabled the capture engine is not idle, it is not
running at all, so a manual take starts it. Two consequences handled here:

  - It is released again when the take ends — logged, cancelled, or dropped for
    being a digital mode. An operator who records one contact does not expect
    their microphone held open for the rest of the session. The release is a
    deferred call at the top of the save path so every exit goes through it,
    rather than one that has to be remembered at each return.
  - There is no pre-roll. An automatic recording opens with the seconds BEFORE
    the callsign was typed; a manual one can only begin now. The button's
    tooltip says so, because otherwise the difference between two files is a
    mystery to the person holding them.

The button only appears where it can work: devices configured, automatic
recording off, and a mode whose audio is worth keeping. That state is asked of
the backend rather than inferred from a preference in the interface, so the two
cannot drift apart, and it is re-read when settings are saved.

frontend/wailsjs/go/main/App.d.ts

@@ -749,6 +749,10 @@ export function QSOAudioBegin():Promise<boolean>;
 
 export function QSOAudioCancel():Promise<void>;
 
+export function QSOAudioManualReady():Promise<boolean>;
+
+export function QSOAudioManualStart():Promise<boolean>;
+
 export function QSOAudioResetClock():Promise<boolean>;
 
 export function QSOAudioRestart():Promise<boolean>;

frontend/wailsjs/go/main/App.js

@@ -1446,6 +1446,14 @@ export function QSOAudioCancel() {
   return window['go']['main']['App']['QSOAudioCancel']();
 }
 
+export function QSOAudioManualReady() {
+  return window['go']['main']['App']['QSOAudioManualReady']();
+}
+
+export function QSOAudioManualStart() {
+  return window['go']['main']['App']['QSOAudioManualStart']();
+}
+
 export function QSOAudioResetClock() {
   return window['go']['main']['App']['QSOAudioResetClock']();
 }