[client] egl: restore effects for PQ frames

PQ sources excluded every external filter from the post-process chain.
Decode PQ/BT.2020 into FP16 linear scRGB before active effects and pass
the resulting transfer state to the desktop shader.

Keep the raw PQ path when no effect is active. This avoids adding a
conversion pass or per-frame latency to the common case.

client/renderers/EGL/CMakeLists.txt

@@ -60,6 +60,7 @@ build_shaders(
   shader/hdr_compose.vert
   shader/hdr_compose.frag
   shader/basic.vert
+  shader/hdr_decode.frag
   shader/convert_24bit.frag
   shader/ffx_cas.frag
   shader/ffx_fsr1_easu.frag
@@ -97,6 +98,7 @@ add_library(renderer_EGL STATIC
   ffx.c
   filter_glsl.c
   filter_24bit.c
+  filter_hdr.c
   filter_ffx_cas.c
   filter_ffx_fsr1.c
   filter_downscale.c