feat(voice-client): PySide6 desktop client and Windows build scripts

Add voice_confirmation_client (poll, TTS MP3 playback, mic WAV resolve),
PyInstaller spec, start/build helpers, and API unit tests.

Pending manual testing: end-to-end on OR workstations and packaged exe.

Made-with: Cursor

scripts/build_voice_client.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+"""Build the voice confirmation desktop client with PyInstaller (run on target OS)."""
+
+from __future__ import annotations
+
+import argparse
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+
+
+def main() -> None:
+    root = Path(__file__).resolve().parents[1]
+    spec = root / "voice_client.spec"
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--clean",
+        action="store_true",
+        help="Remove build/ and dist/ before building",
+    )
+    args = parser.parse_args()
+    if args.clean:
+        for name in ("build", "dist"):
+            p = root / name
+            if p.is_dir():
+                shutil.rmtree(p)
+    if not spec.is_file():
+        print(f"Missing {spec}", file=sys.stderr)
+        sys.exit(1)
+    cmd = [sys.executable, "-m", "PyInstaller", str(spec), "--noconfirm"]
+    print("Running:", " ".join(cmd))
+    raise SystemExit(subprocess.call(cmd, cwd=root))
+
+
+if __name__ == "__main__":
+    main()