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/rtsp.rs

@@ -357,12 +357,17 @@ fn stream_config(map: &HashMap<String, String>) -> Option<StreamConfig> {
         Some("2") => Codec::Av1,
         _ => Codec::H264,
     };
-    // 10-bit/HDR request flag. We never advertise the Main10 SCM bits, so a compliant
-    // client can't ask — if one does anyway, stream 8-bit SDR rather than failing.
-    if parse_u("x-nv-video[0].dynamicRangeMode").unwrap_or(0) != 0 {
+    // 10-bit/HDR request (Moonlight sets `dynamicRangeMode != 0` only when it both saw our Main10 SCM
+    // bit AND the user enabled HDR). Honor it only when the host can actually deliver Main10 (Windows +
+    // PUNKTFUNK_10BIT, `host_hdr_capable`); when honored, the video path proactively enables advanced
+    // color on the virtual display so a PQ stream flows even from an SDR desktop. A request we can't
+    // honor degrades to 8-bit SDR (and a desktop that is ALREADY HDR still streams PQ regardless, since
+    // the IDD-push capturer follows the display).
+    let hdr_requested = parse_u("x-nv-video[0].dynamicRangeMode").unwrap_or(0) != 0;
+    let hdr = hdr_requested && crate::gamestream::host_hdr_capable();
+    if hdr_requested && !hdr {
         tracing::warn!(
-            "client requested HDR/10-bit (dynamicRangeMode != 0) — not advertised/supported, \
-             streaming 8-bit SDR"
+            "client requested HDR (dynamicRangeMode != 0) but host is not HDR-capable — streaming 8-bit SDR"
         );
     }
     // Parity floor the client asks for (protects small frames); clamp to a sane max.
@@ -377,6 +382,7 @@ fn stream_config(map: &HashMap<String, String>) -> Option<StreamConfig> {
         bitrate_kbps,
         codec,
         min_fec,
+        hdr,
     })
 }