feat(windows-host): mic passthrough — auto-wire audio devices + bundle VB-CABLE

The Windows virtual mic worked only with manual Sound-settings fiddling: on a
headless host (no real audio output) BOTH the desktop-audio loopback and the
virtual mic must run on virtual cables, and on DIFFERENT ones or the loopback
re-captures the injected mic (echo). The Steam pair gives only one usable cable
(Steam Streaming Speakers loopback is silent — validated), so the mic + loopback
collided and echoed, and when the default playback happened to be the mic device
the anti-echo guard reported the mic "unavailable".

Host now auto-wires the devices at startup (audio/windows/audio_control.rs,
ensure_wired_once, hooked from open_audio_capture/open_virtual_mic): default
playback = a loopback-capable render that is NOT a cable and NOT the dead Steam
Speakers (real output > Steam Streaming Microphone); default recording = the mic
capture (VB-Cable "CABLE Output" preferred). Uses a hand-rolled IPolicyConfig
vtable (the only way to set a default endpoint; not in windows/wasapi crates).
Opt out with PUNKTFUNK_KEEP_DEFAULT. wasapi_mic candidates now prefer "cable
input". Validated live: from a deliberately-wrong start (playback=CABLE Input)
the host corrected both default endpoints at the OS level.

A Windows audio endpoint can only be created by a kernel-mode driver (no UMDF
path — ACX is KMDF-only), so we cannot self-sign our own like the UMDF gamepad/
display drivers. Instead the installer bundles + silently installs the official
base VB-CABLE (VB-Audio donationware, vendor-signed → loads with no test-signing,
redistributed under VB-Audio's bundling grant): install-vbcable.ps1 (seed the
VB-Audio cert into TrustedPublisher, run -i -h) + an installaudiocable task,
gated on -VbCableDir/$env:VBCABLE_DIR (the package binary is not in the repo).
Attribution in packaging/windows/licenses/VB-CABLE-NOTICE.txt. .iss compiles
with the path enabled.

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

crates/punktfunk-host/src/audio.rs

@@ -42,6 +42,7 @@ pub fn open_audio_capture(channels: u32) -> Result<Box<dyn AudioCapturer>> {
 
 #[cfg(target_os = "windows")]
 pub fn open_audio_capture(channels: u32) -> Result<Box<dyn AudioCapturer>> {
+    audio_control::ensure_wired_once();
     wasapi_cap::WasapiLoopbackCapturer::open(channels)
         .map(|c| Box::new(c) as Box<dyn AudioCapturer>)
 }
@@ -77,6 +78,7 @@ pub fn open_virtual_mic(channels: u32) -> Result<Box<dyn VirtualMic>> {
 
 #[cfg(target_os = "windows")]
 pub fn open_virtual_mic(channels: u32) -> Result<Box<dyn VirtualMic>> {
+    audio_control::ensure_wired_once();
     wasapi_mic::WasapiVirtualMic::open(channels).map(|m| Box::new(m) as Box<dyn VirtualMic>)
 }
 
@@ -85,6 +87,9 @@ pub fn open_virtual_mic(_channels: u32) -> Result<Box<dyn VirtualMic>> {
     anyhow::bail!("virtual mic requires Linux + PipeWire or Windows + a virtual audio device")
 }
 
+#[cfg(target_os = "windows")]
+#[path = "audio/windows/audio_control.rs"]
+mod audio_control;
 #[cfg(target_os = "linux")]
 mod linux;
 #[cfg(target_os = "windows")]