Audio cues: add send/receive on-off and minimise/restore cues (2 sounds each), drop .sfk byproducts

Six new machine-wide cues, each with the same numbered-variant + Preferences treatment as
the others (enable tickbox, Choose default sound picker, Play/Browse):

- Send turned on / off, Receive turned on / off: fire from OnStreamingCheckboxChanged, so
  they sound whether the user clicked the in-window tickbox or pressed the mute shortcut
  (the hotkey flips .Checked, which routes through the same handler). Suppressed during
  profile load by the existing password-gate guard, so loading a profile doesn't blast them.
- Minimise (hide) / Restore (show): fire from the tray controller's Minimize()/Restore() on a
  genuine visibility transition (guarded against no-op / startup-minimise).

Enable flags + custom-WAV overrides for these six live machine-wide in AppConfig
(EnableSendOnCue.., MachineCueCustomPaths) - they're app-level feedback, not per-profile
audio - so no Profile/settings-cache plumbing. TryLoadCueSound now also honours the
machine-wide custom path. PreferencesDialog gains a MachineRow helper + the six rows.

Sounds: shipped via the existing sounds\*.wav wildcard. Fixed an obvious typo in the
supplied files ("rcieve off 1.wav" -> "recieve off 1.wav") so receive-off has both variants.
Renamed the old single-name cue WAVs to Ed's numbered-variant set; added key/passkey and the
new cue sounds.

build-release.ps1: new step deletes the SoundForge .sfk peak-file byproducts from sounds\
before packaging (they never shipped - build is *.wav only - this just keeps the tree tidy).

Tests + manual updated for the six new cues.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

MANUAL.md

@@ -866,7 +866,7 @@ Toggle| What it does
 
 ## 18. Audio cue sounds
 
-RemSound plays a short sound at moments where you might want an audible confirmation that something just happened. These are called **cue sounds**. Nine events have a cue:
+RemSound plays a short sound at moments where you might want an audible confirmation that something just happened. These are called **cue sounds**. Fifteen events have a cue:
 
 Cue| Plays when
 ---|---
@@ -879,6 +879,10 @@ Cue| Plays when
 **Profile menu open sound**|  The Quick profile switch popup opens.
 **Update sound**|  An update is about to install — it plays just before RemSound closes to update itself. Handy when updates install silently in the background, so you're not caught off guard when RemSound restarts. Plays whether you ran the update by hand or it installed on its own.
 **Startup sound**|  RemSound has finished starting up. It plays once at launch, even when RemSound opens straight to the notification area, so you know it's running.
+**Send turned on / off sound**|  You turn sending your audio on or off — whether by ticking the **Send my audio** box in the window or by pressing its mute shortcut. There's a separate sound for on and for off.
+**Receive turned on / off sound**|  You turn receiving audio on or off — from the **Receive audio** box or its mute shortcut. Again, a separate sound for on and for off.
+**Minimise (hide) sound**|  RemSound's window minimises to the notification area (hides).
+**Restore (show) sound**|  RemSound's window is brought back from the notification area (shows).
 
 All of these cues play through your default Windows sound output, which is separate from the audio RemSound is sending or receiving. They don't appear in a normal recording. (The exception: if your sending side is capturing the very output device the cues play through, then they get captured along with everything else from that device.)