feat: known-good CPU audio + 1080p VAAPI + KMS display wall

Working snapshot before the OpenVINO MetricGAN GPU spike:
thread-capped SpeechBrain DelaySum+MetricGAN on CPU, hop 200 ms,
video hold for A/V sync, Arc VAAPI H.264, headless kmssink wall.
32 tests passing. Do not treat this as a GPU audio path.

scripts/speaker_invite.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Print a LiveKit Meet URL + token so a speaker can join and share a screen.
+
+STUB / future: do not use until the production LiveKit server is online.
+The third display currently shows a placeholder only.
+"""
+from __future__ import annotations
+
+import argparse
+import sys
+from pathlib import Path
+from urllib.parse import quote, urlparse
+
+ROOT = Path(__file__).resolve().parents[1]
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+from config import load_config
+from tokens import make_speaker_token
+
+
+def public_url(cfg) -> str:
+    if cfg.livekit_public_url:
+        return cfg.livekit_public_url.rstrip("/")
+    parsed = urlparse(cfg.url)
+    host = parsed.hostname or "127.0.0.1"
+    if host in ("127.0.0.1", "localhost"):
+        host = "10.200.0.20"
+    scheme = parsed.scheme or "ws"
+    port = parsed.port
+    if port:
+        return f"{scheme}://{host}:{port}"
+    return f"{scheme}://{host}"
+
+
+def main() -> int:
+    ap = argparse.ArgumentParser(description=__doc__)
+    ap.add_argument("--identity", default="", help="default: DISPLAY_SPEAKER_PARTICIPANT")
+    ap.add_argument("--name", default="Speaker")
+    args = ap.parse_args()
+    cfg = load_config()
+    identity = args.identity or cfg.display_speaker_participant or "speaker"
+    token = make_speaker_token(cfg.api_key, cfg.api_secret, cfg.room, identity, args.name)
+    url = public_url(cfg)
+    meet = (
+        "https://meet.livekit.io/custom"
+        f"?liveKitUrl={quote(url, safe='')}&token={quote(token, safe='')}"
+    )
+    print(f"room:     {cfg.room}")
+    print(f"identity: {identity}")
+    print(f"url:      {url}")
+    print(f"token:    {token}")
+    print()
+    print("Open this on the speaker laptop, then Share screen:")
+    print(meet)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())