feat(gamestream): AV1 negotiation + 5.1/7.1 surround audio

Codec negotiation (M2 polish):
- ServerCodecModeSupport now advertises what we encode: H264|HEVC|AV1_MAIN8
  = 65793 (flags verified against moonlight-common-c Limelight.h). The old
  placeholder 3843 wrongly claimed HEVC Main10 + 4:4:4 and no AV1. Main10
  bits stay off on purpose: Moonlight ties 10-bit to HDR, and capture is
  8-bit SDR BGRx with no HDR metadata path (av1_nvenc -highbitdepth was
  validated working for later).
- RTSP ANNOUNCE: bitStreamFormat 0/1/2 -> H264/HEVC/AV1 (already plumbed to
  av1_nvenc; validated e2e via `m0 --codec av1` + ffprobe av01), and a
  dynamicRangeMode!=0 request now logs + falls back to 8-bit SDR.

Surround audio (M2 polish):
- ANNOUNCE x-nv-audio.surround.{numChannels,AudioQuality} +
  x-nv-aqos.packetDuration -> per-session AudioParams; DESCRIBE advertises
  all six Opus configs (normal before HQ per channel count). Normal-quality
  mappings are pre-rotated for the client's GFE-order LFE swap
  (RtspConnection.c, verified verbatim) so its derived decoder mapping
  equals our encoder mapping — including 7.1, where Sunshine's rotate only
  covers [3,6) and scrambles LFE/SL/SR.
- 5.1/7.1 encode via libopus multistream (audiopus_sys, the sys layer the
  opus crate already links) with Sunshine's layouts/bitrates, RAII wrapper;
  the live-validated stereo wire is byte-identical (plain Opus, no FEC).
- Surround sessions add Sunshine-style RS(4,2) audio FEC (packetType 127 +
  AUDIO_FEC_HEADER, the OpenFEC parity matrix both ends hardcode, nanors
  gemm semantics verified from nanors/rs.c).
- PipeWire capture generalized to the negotiated channel count with explicit
  FL FR FC LFE RL RR [SL SR] positions; missing sink channels are zero-
  filled by the channel-mixer. PwAudioCapturer now tears down cleanly on
  Drop (pipewire channel -> loop quit), so a channel-count change can
  reopen without leaking a capture stream.

Tests: serverinfo mask, RTSP codec/audio param parsing, DESCRIBE contents,
surround-params strings + client-swap round trip, FEC parity self-recovery
and packet layout, real-codec 5.1 channel-identity round trip, and an
ignored live test (ran green against a 6ch null sink monitor).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/gamestream/serverinfo.rs

@@ -40,3 +40,40 @@ pub fn serverinfo_xml(host: &Host, https: bool) -> String {
         local_ip = host.local_ip,
     )
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::gamestream::{SCM_AV1_MAIN8, SCM_H264, SCM_HEVC, SCM_HEVC_MAIN10};
+
+    /// The advertised codec mask: H.264 + HEVC + AV1 Main8 (= 65793), and explicitly *no*
+    /// 10-bit bits — Moonlight gates its HDR mode on those, which we can't deliver (8-bit
+    /// SDR capture). Flag values are moonlight-common-c `Limelight.h`.
+    #[test]
+    fn codec_mode_support_mask() {
+        assert_eq!(SERVER_CODEC_MODE_SUPPORT, 0x1 | 0x100 | 0x10000);
+        assert_eq!(SERVER_CODEC_MODE_SUPPORT, 65793);
+        assert_eq!(
+            SERVER_CODEC_MODE_SUPPORT & SCM_HEVC_MAIN10,
+            0,
+            "no 10-bit/HDR claim"
+        );
+        assert_eq!(
+            SERVER_CODEC_MODE_SUPPORT,
+            SCM_H264 | SCM_HEVC | SCM_AV1_MAIN8
+        );
+    }
+
+    #[test]
+    fn serverinfo_xml_carries_codec_mask() {
+        let host = Host {
+            hostname: "test".into(),
+            uniqueid: "uid".into(),
+            local_ip: std::net::IpAddr::V4(std::net::Ipv4Addr::LOCALHOST),
+            http_port: 47989,
+            https_port: 47984,
+        };
+        let xml = serverinfo_xml(&host, false);
+        assert!(xml.contains("<ServerCodecModeSupport>65793</ServerCodecModeSupport>"));
+    }
+}