fix(host/security): close audit findings S1,#1,#4,#10,#12,#7,#6,S2-S6 (Linux/cross-platform)

Remediations from design/security-review-2026-06-28.md verified on Linux
(cargo check/clippy/test green; Windows-gated paths verify in CI):

- S1 [HIGH]: bump quinn-proto 0.11.14 -> 0.11.15 (RUSTSEC-2026-0185,
  pre-auth out-of-order STREAM reassembly memory exhaustion on the
  always-on default QUIC listener).
- #1 [HIGH]: remove the unauthenticated nvhttp `GET /pin` endpoint; the
  GameStream PIN is delivered ONLY via the bearer-gated mgmt API, so a
  network client can no longer submit its own displayed PIN and self-pair.
- #4 [HIGH->MED]: gate the unauthenticated RTSP/UDP media plane on a paired
  `/launch` and bind it to the launching client's source IP (threaded
  through the HTTPS handler), so an unpaired peer can neither start capture
  on an idle host nor ride a paired client's active launch.
- #12: bound concurrent parked pairing waiters (MAX_PARKED_WAITERS) so a
  pre-auth peer can't pin unbounded 300s handshakes. +regression test.
- #10: throttle the per-packet ENet control GCM-decrypt-failed warn
  (exponential backoff) so a junk flood can't spam the log.
- #7 [MED->LOW]: serialize all process-global env mutation on the
  session-setup path under a new vdisplay::ENV_LOCK (apply_session_env /
  apply_input_env / the launch-cmd set_var / the gamescope env read), so
  concurrent native sessions can't race set_var/getenv (data-race UB ->
  host-wide DoS). Full per-session SessionContext threading remains a
  follow-up for cross-session value confusion.
- #6 [MED]: move the gamescope EIS socket relay from world-writable /tmp to
  $XDG_RUNTIME_DIR (per-user 0700) and reject a symlinked relay file, so a
  local user can't intercept (keylog) or deny the remote session's input.
- S2: a malformed client Opus mic frame now drops that frame instead of
  tearing down the shared host-lifetime virtual mic (cross-session DoS).
- S3: track held buttons/keys in capped HashSets (was unbounded Vec with
  O(n) scans) so a paired client can't grow per-session input state.
- S5: reject fps==0/absurd at the open_video chokepoint (covers Hello,
  ANNOUNCE, Reconfigure) so the encoder time_base/pts math can't div-by-0.
- S6: bound the shared mic mpsc (drop-newest when full).
- S4: cap Epic launcher-cache reads (catcache.bin/.item) so a planted giant
  can't OOM the host during library enumeration.

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

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

@@ -24,6 +24,12 @@ use std::sync::Arc;
 #[derive(Clone)]
 pub(crate) struct PeerCertFingerprint(pub Option<String>);
 
+/// The TCP source address of an HTTPS request, injected per-connection by [`serve_https`]. Used by
+/// `/launch` to record which paired client owns the session so the unauthenticated RTSP/UDP media
+/// plane can bind to that peer's IP (security-review 2026-06-28 #4).
+#[derive(Clone, Copy)]
+pub(crate) struct PeerAddr(pub SocketAddr);
+
 /// HTTPS server that surfaces the verified client cert to handlers. `axum_server` can't expose the
 /// peer cert, so this runs the rustls handshake itself (tokio-rustls), reads the peer certificate,
 /// and serves the axum `Router` over hyper with the peer's fingerprint attached to every request as
@@ -39,7 +45,7 @@ pub(crate) async fn serve_https(
         .await
         .with_context(|| format!("bind HTTPS {bind}"))?;
     loop {
-        let (tcp, _peer) = match listener.accept().await {
+        let (tcp, peer) = match listener.accept().await {
             Ok(v) => v,
             Err(e) => {
                 tracing::warn!(error = %e, "HTTPS accept failed");
@@ -63,14 +69,16 @@ pub(crate) async fn serve_https(
                 .peer_certificates()
                 .and_then(|c| c.first())
                 .map(|c| hex::encode(punktfunk_core::quic::endpoint::cert_fingerprint(c.as_ref())));
-            let peer = PeerCertFingerprint(fp);
+            let fp = PeerCertFingerprint(fp);
+            let addr = PeerAddr(peer);
             let svc =
                 hyper::service::service_fn(move |req: hyper::Request<hyper::body::Incoming>| {
                     let app = app.clone();
-                    let peer = peer.clone();
+                    let fp = fp.clone();
                     async move {
                         let mut req = req.map(axum::body::Body::new);
-                        req.extensions_mut().insert(peer);
+                        req.extensions_mut().insert(fp);
+                        req.extensions_mut().insert(addr);
                         app.oneshot(req).await // Router error is Infallible
                     }
                 });