Cycle the Windows default audio output from a global hotkey

A single 306 KB GUI-subsystem binary with no tray icon and no settings
window: one hidden popup owns the hotkey, the device-change callbacks and
the flyout, and the process sleeps in GetMessageW at 0% CPU in between.

Windows exposes no public API for setting the default audio endpoint, so
this uses the undocumented IPolicyConfig COM interface, confined to
src/policy.rs. Verified working on build 26200. Everything else -
enumeration, IMMNotificationClient, RegisterHotKey, the flyout - is
documented Win32.

The flyout uses the DWM acrylic backdrop and rounded corners the shell
uses for its own flyouts, with text drawn via DrawThemeTextEx and
DTT_COMPOSITED into a 32-bpp DIB, which is what keeps GDI from leaving
black fringes on a composited surface.

Console and Multimedia roles move by default; Communications stays put so
voice chat keeps its headset. Config is a hand-parsed INI reloaded on the
next keypress, keeping the dependency list to the windows crate alone.

Built by cross-compiling from a devcontainer with mingw-w64, so nothing is
installed on the Windows host and the exe imports only system DLLs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/deploy.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+#
+# Copy the cross-compiled exe to a real Windows path and (re)start it.
+#
+# Run this on the WSL host, NOT inside the devcontainer: the container has no Windows
+# interop, so it can build the binary but cannot launch it. Copying to %LOCALAPPDATA%
+# rather than launching over \\wsl.localhost avoids zone-of-origin and file-locking
+# quirks on the WSL share.
+set -euo pipefail
+
+repo="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+exe="$repo/target/x86_64-pc-windows-gnu/release/audioswitch.exe"
+
+if [ ! -f "$exe" ]; then
+	echo "No binary. Build it first:  cargo build --release" >&2
+	exit 1
+fi
+
+dest_win="$(cmd.exe /c 'echo %LOCALAPPDATA%' 2>/dev/null | tr -d '\r')\\AudioSwitch"
+dest="$(wslpath -u "$dest_win")"
+mkdir -p "$dest"
+
+# Stop whatever is running, or the copy fails with the file locked.
+if [ -f "$dest/audioswitch.exe" ]; then
+	"$dest/audioswitch.exe" --quit >/dev/null 2>&1 || true
+	sleep 0.5
+fi
+
+cp "$exe" "$dest/audioswitch.exe"
+
+# `cmd.exe /c start` hangs forever under WSL interop here, so launch through PowerShell,
+# which detaches cleanly. The cd avoids cmd/powershell complaining about a UNC cwd.
+(cd /mnt/c && powershell.exe -NoProfile -Command \
+	"Start-Process -FilePath '${dest_win}\\audioswitch.exe'") </dev/null >/dev/null 2>&1
+
+echo "Deployed and started: ${dest_win}\\audioswitch.exe"