feat(gamestream): advertise HDR + surface the game library (with covers) to Moonlight

Bring the GameStream/Moonlight plane up to the native plane's capability parity.

HDR (Windows only):
- New host_hdr_capable() gate (Windows + PUNKTFUNK_10BIT, matching the native
  policy). serverinfo layers SCM_HEVC_MAIN10 onto the probed/static codec mask, so
  Moonlight finally offers its HDR toggle (live: mask 0x10101 -> 0x10301).
- Parse the client's dynamicRangeMode into StreamConfig.hdr and pass it through to
  OutputFormat::resolve, so a client HDR request proactively enables advanced color
  on the per-session virtual display (PQ flows even from an SDR desktop). The
  encoder bit depth now derives from the captured frame format (gs_bit_depth) rather
  than a hard-coded 8 that mislabeled the already-Main10 HDR stream.

Game library in /applist:
- The catalog now layers library::all_games() (Steam/Epic/GOG/Xbox/custom) on top of
  Desktop/apps.json, each with a STABLE GameStream id (FNV-1a, dedup-probed) and the
  store-qualified library id. Launch routes through the existing security-reviewed
  launch_title/launch_command via library::launch_gamestream_library — a client can
  only pick an existing title, never inject a command.
- /appasset cover proxy: Moonlight fetches per-app covers from the host, so resolve
  appid -> library cover URL and proxy the bytes (portrait -> header -> hero -> logo;
  data: + bounded http(s) fetch), on a blocking thread. IsHdrSupported reflects the
  host HDR capability.

4:4:4 stays off on GameStream by design: stock Moonlight is 4:2:0 and the Windows
IDD-push capturer can't deliver full chroma yet (capturer_supports_444() == false);
the gate is documented so it lights up once IDD-push full-chroma capture lands.

Validated live (Moonlight -> Windows NVENC host): HDR advertised, the Epic library
shows with covers, launch works. clippy clean; apps/serverinfo/library unit tests
cover the HDR mask, stable-id, dedup, and data-URL paths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -43,11 +43,33 @@ pub fn serverinfo_xml(host: &Host, https: bool, paired: bool) -> String {
     )
 }
 
-/// The `<ServerCodecModeSupport>` mask to advertise. On the VAAPI (AMD/Intel) backend it reflects
-/// what the GPU can ACTUALLY encode (probed — AV1 is narrow, and an old iGPU might lack HEVC), so a
-/// Moonlight client never negotiates a codec the encoder can't open. NVENC and Windows keep the
-/// Moonlight-validated static superset.
+/// The `<ServerCodecModeSupport>` mask to advertise: the SDR baseline ([`base_codec_mode_support`]) plus
+/// the HEVC Main10 (HDR) bit when the host can actually deliver HDR ([`apply_hdr`] /
+/// [`crate::gamestream::host_hdr_capable`]). Without the Main10 bit Moonlight never offers its HDR
+/// toggle; with it, enabling HDR client-side negotiates Main10 and the IDD-push path streams BT.2020 PQ.
 fn codec_mode_support() -> u32 {
+    apply_hdr(
+        base_codec_mode_support(),
+        crate::gamestream::host_hdr_capable(),
+    )
+}
+
+/// Add the HEVC Main10 (HDR) bit to `base` when `hdr` and HEVC is advertised — pure so the
+/// HDR-layering is unit-testable without a GPU. (HDR streaming uses HEVC Main10; AV1 Main10 is left
+/// off until the GameStream AV1 path is live-confirmed.)
+fn apply_hdr(base: u32, hdr: bool) -> u32 {
+    if hdr && base & super::SCM_HEVC != 0 {
+        base | super::SCM_HEVC_MAIN10
+    } else {
+        base
+    }
+}
+
+/// The **SDR baseline** mask. On the VAAPI (AMD/Intel) backend it reflects what the GPU can ACTUALLY
+/// encode (probed — AV1 is narrow, and an old iGPU might lack HEVC), so a Moonlight client never
+/// negotiates a codec the encoder can't open. NVENC and the GPU-less software path keep the
+/// Moonlight-validated static superset. HDR (Main10) is layered on by [`codec_mode_support`].
+fn base_codec_mode_support() -> u32 {
     #[cfg(target_os = "linux")]
     if crate::encode::linux_zero_copy_is_vaapi() {
         if let Some(m) = probed_mask(crate::encode::vaapi_codec_support()) {
@@ -108,6 +130,22 @@ mod tests {
         );
     }
 
+    #[test]
+    fn apply_hdr_adds_main10_only_when_capable_and_hevc() {
+        // HDR-capable + HEVC advertised → Main10 added.
+        assert_eq!(
+            apply_hdr(SCM_H264 | SCM_HEVC | SCM_AV1_MAIN8, true),
+            SCM_H264 | SCM_HEVC | SCM_AV1_MAIN8 | SCM_HEVC_MAIN10
+        );
+        // Not HDR-capable → baseline unchanged (no HDR claim).
+        assert_eq!(
+            apply_hdr(SCM_H264 | SCM_HEVC | SCM_AV1_MAIN8, false),
+            SCM_H264 | SCM_HEVC | SCM_AV1_MAIN8
+        );
+        // HDR-capable but a GPU with no HEVC at all → no Main10 (you can't do Main10 without HEVC).
+        assert_eq!(apply_hdr(SCM_H264, true), SCM_H264);
+    }
+
     #[test]
     fn serverinfo_xml_carries_codec_mask() {
         let host = Host {