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/windows/wasapi_mic.rs

@@ -4,10 +4,12 @@
 //! **capture** endpoint then surfaces as a microphone that host apps can record from.
 //!
 //! Target device, by friendly-name substring (first match wins; override with `PUNKTFUNK_MIC_DEVICE`):
-//! "Steam Streaming Microphone" (ships with Steam Remote Play — exactly this purpose), VB-Audio
-//! "CABLE Input", VoiceMeeter, or anything with "virtual" in the name. If none is present we
-//! auto-install the Steam Streaming audio pair (see [`install_steam_audio_pair`]); failing that we
-//! return an error with install guidance and the host runs without mic passthrough.
+//! VB-Audio "CABLE Input" (bundled by the installer — the preferred, dedicated mic target), the
+//! "Steam Streaming Microphone", VoiceMeeter, or anything with "virtual" in the name.
+//! [`super::audio_control`] sets the default playback to a DIFFERENT loopback-capable device so the
+//! chosen mic is never the endpoint the loopback captures. If no candidate is present we auto-install
+//! the Steam Streaming audio pair (see [`install_steam_audio_pair`]); failing that we return an error
+//! with install guidance and the host runs without mic passthrough.
 //!
 //! **Anti-echo guard (the whole point of this being non-trivial).** The desktop-audio plane
 //! ([`super::wasapi_cap`]) loopback-captures the **default render endpoint**. WASAPI loopback
@@ -45,8 +47,8 @@ const MAX_QUEUE_BYTES: usize = (SAMPLE_RATE as usize * 80 / 1000) * BLOCK_ALIGN;
 /// Render-endpoint friendly-name substrings (lowercased) we can write into so the device's capture
 /// endpoint becomes a host mic. Ordered by preference.
 const CANDIDATES: &[&str] = &[
+    "cable input", // VB-Audio Virtual Cable — bundled by the installer; the preferred dedicated mic target
     "steam streaming microphone",
-    "cable input",
     "voicemeeter input",
     "voicemeeter aux input",
     "virtual",