feat(host): Apollo-backlog hardening — cert gate, NVENC RFI, media QoS, async injector

A pass over the apollo-comparison backlog (re-verified against current code).
Lands four items end-to-end plus a Windows-DualSense scoping doc.

- #5/#92/#26 — GameStream paired-cert allow-list. tls.rs surfaces the verified
  peer cert to handlers (serve_https + PeerCertFingerprint, now shared with the
  mgmt API instead of duplicated); nvhttp gates /launch /resume /applist /cancel
  on AppState.paired and reports a real PairStatus; save_paired writes atomically
  (temp+rename). Closes the "mTLS accepts any client cert" hole. + regression test.

- #6/#51/#19/#22 — NVENC caps query -> reference-frame invalidation. nvenc.rs
  query_caps probes nvEncGetEncodeCaps (max dims / 10-bit / custom-VBV / RFI),
  rejecting over-range modes and degrading 10-bit->8-bit instead of an opaque
  InvalidParam. New Encoder::invalidate_ref_frames (default false -> caller
  keyframes); the Windows NVENC path implements real RFI (multi-ref DPB +
  nvEncInvalidateRefFrames, dedup + IDR-on-overflow). control.rs decodes the
  0x0301 lost-frame range (Apollo's IDX_INVALIDATE_REF_FRAMES) -> AppState.rfi_range
  -> encode loop, falling back to a keyframe. NOTE: the Windows NVENC impl is
  RTX-box/CI-pending (can't compile on Linux); adversarially reviewed vs the SDK.

- #43/#72 — media socket QoS + buffer growth. New punktfunk_core::transport::qos:
  grow_socket_buffers (factored out the native plane's 32MB SO_SNDBUF growth so the
  GameStream sockets reuse it) + set_media_qos (opt-in PUNKTFUNK_DSCP=1: DSCP CS5
  video / CS6 audio + Linux SO_PRIORITY, Apollo's scheme). Wired into UdpTransport
  and the GameStream video/audio sockets. Windows IP_TOS needs qWAVE (follow-up).

- #8/#45 — GameStream input injection off the ENet service thread. on_receive no
  longer injects inline (a slow inject head-blocked ENet keepalive/retransmit); it
  forwards to a dedicated injector thread. The hardened InjectorService moved from
  punktfunk1 into crate::inject (shared by both planes) + a coalesce step that sums
  adjacent relative-mouse/scroll deltas while preserving button/key/abs ordering.

Docs: re-verified apollo-comparison.md status (22 items already done/obsolete since
the snapshot) + windows-dualsense-scoping.md (ViGEm can't emulate a DualSense; real
DS5 on Windows needs a VHF virtual-HID driver — web-research pass pending).

fmt + clippy -D warnings clean; full workspace test suite green; no C-ABI/OpenAPI drift.

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

crates/punktfunk-host/src/encode.rs

@@ -57,6 +57,16 @@ pub trait Encoder: Send {
     /// Force the next submitted frame to be an IDR keyframe (e.g. after a client
     /// reference-frame-invalidation request). Default: no-op.
     fn request_keyframe(&mut self) {}
+    /// Invalidate a contiguous range of previously-encoded reference frames (client frame numbers,
+    /// as reported in a loss-recovery request) so the encoder re-references an older still-valid
+    /// frame instead of emitting a full IDR. Returns `true` if a real reference invalidation was
+    /// performed; `false` means the encoder couldn't (range older than the DPB, or the backend has
+    /// no RFI) and the caller should fall back to [`request_keyframe`](Self::request_keyframe).
+    /// Default: `false` — only the Windows direct-NVENC path implements true RFI; libavcodec
+    /// (Linux NVENC) and VAAPI can't express `nvEncInvalidateRefFrames`, so they keyframe.
+    fn invalidate_ref_frames(&mut self, _first_frame: i64, _last_frame: i64) -> bool {
+        false
+    }
     /// Pull the next encoded AU if one is ready.
     fn poll(&mut self) -> Result<Option<EncodedFrame>>;
     /// Signal end-of-stream. After this, drain the remaining AUs with [`poll`](Self::poll)