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>

src/RemSound.App/SelfTest.cs

@@ -303,7 +303,11 @@ internal static class SelfTest
         Check(Directory.Exists(soundsDir), "the runtime sounds folder must exist (cues are consolidated at startup)");
         // Cues ship as numbered variants ("connect 1.wav", ...); each required cue must have at
         // least one variant present.
-        foreach (var cue in new[] { "connect.wav", "disconnect.wav", "start up.wav" })
+        foreach (var cue in new[]
+        {
+            "connect.wav", "disconnect.wav", "start up.wav",
+            "send on.wav", "send off.wav", "recieve on.wav", "recieve off.wav", "minimise.wav", "maximise.wav",
+        })
         {
             Check(CueSounds.Variants(cue).Count > 0,
                 $"no sound variant present for the '{Path.GetFileNameWithoutExtension(cue)}' cue (was the shipped sounds\\ folder empty?)");