h264: V3D shader for deblock_luma_h — first QPU port since cycle 9

Ports cycle 8's v3d_h264deblock.comp (V edge, horizontal across a row)
to the H orientation (V edge, horizontal across a column).  Same
algorithm, transposed access pattern:

  V variant: lane → column, reads/writes pix[±N*stride] (vertical I/O)
  H variant: lane → row,    reads/writes pix[±N]        (horizontal I/O)

  WG geometry unchanged: 256 invocations, 16 edges/WG, 16 lanes/edge.
  Lane-in-edge interpretation flips: column-index for V → row-index
  for H.  tc0 segment math unchanged (one tc0 byte per 4 lanes).
  dst_max calculation flips: V used dst_off + 3*stride + 16 (cols),
  H uses dst_off + 15*stride + 4 (rows).

Recipe table: DAEDALUS_KERNEL_H264_DEBLOCK_LH = QPU (was CPU).  AUTO
dispatch now picks QPU for the H edge as well as the V edge.  CPU
NEON path stays as the explicit-SUBSTRATE_CPU + has_qpu=0 fallback.

Verified on hertz (Pi 5 / V3D 7.1):

  $ ./build/test_api_h264 | grep luma_h
    H264_DEBLOCK_LH recipe substrate: 2     (was 1 — flipped to QPU)
    H.264 deblock luma h: 1024/1024 bytes bit-exact (100.0000%)

Bit-exact against the C reference (h264_h_loop_filter_luma_ref) on
8 tiles × 8 cols × 16 rows of random input.  Same correctness gate
as the cycle 8 V shader.

CMake plumbing: glslang rule for v3d_h264deblock_h.comp; new SPV
added to daedalus_shaders ALL list + install rule.  daedalus_ctx
gains a parallel h264deblock_h_pipe_ready / h264deblock_h_pipe pair
(can't share with V because pipelines bind a specific SPIR-V module
at create time).

What this changes for the substitution arc: PR #97's 0008-h264-
deblock-luma-h substitution patch already plumbed
daedalus_recipe_dispatch_h264_deblock_luma_h through libavcodec.
That path was NEON-by-recipe; with this PR it becomes QPU-by-recipe
(unless the libavcodec ctx is no-QPU per daedalus_ctx_create_no_qpu,
in which case it stays NEON — same shape as cycle 8's V shader).

Coverage state for H.264 8-bit 4:2:0 deblock kernels (QPU shaders):
  luma_v       ✓ cycle 8       ✓ now
  luma_h       —               ✓ THIS PR
  chroma_v/h   —               (CPU NEON; smaller tiles, lower-priority)
  *_intra (4)  —               (CPU NEON; less common)

CMakeLists.txt

@@ -284,6 +284,17 @@ if (DAEDALUS_BUILD_VULKAN)
         VERBATIM
     )
 
+    set(H264DEBLOCK_H_SPV ${CMAKE_BINARY_DIR}/v3d_h264deblock_h.spv)
+    add_custom_command(
+        OUTPUT ${H264DEBLOCK_H_SPV}
+        COMMAND ${GLSLANG_VALIDATOR} -V --target-env vulkan1.3
+                -o ${H264DEBLOCK_H_SPV}
+                ${CMAKE_SOURCE_DIR}/src/v3d_h264deblock_h.comp
+        DEPENDS ${CMAKE_SOURCE_DIR}/src/v3d_h264deblock_h.comp
+        COMMENT "glslang: v3d_h264deblock_h.comp -> v3d_h264deblock_h.spv"
+        VERBATIM
+    )
+
     set(H264_IDCT4_SPV ${CMAKE_BINARY_DIR}/v3d_h264_idct4.spv)
     add_custom_command(
         OUTPUT ${H264_IDCT4_SPV}
@@ -317,7 +328,7 @@ if (DAEDALUS_BUILD_VULKAN)
         VERBATIM
     )
 
-    add_custom_target(daedalus_shaders ALL DEPENDS ${NOOP_SPV} ${IDCT8_SPV} ${LPF_SPV} ${MC_SPV} ${LPF8_SPV} ${CDEF_SPV} ${H264DEBLOCK_SPV} ${H264_IDCT4_SPV} ${H264_IDCT8_SPV} ${H264_QPEL_MC20_SPV})
+    add_custom_target(daedalus_shaders ALL DEPENDS ${NOOP_SPV} ${IDCT8_SPV} ${LPF_SPV} ${MC_SPV} ${LPF8_SPV} ${CDEF_SPV} ${H264DEBLOCK_SPV} ${H264DEBLOCK_H_SPV} ${H264_IDCT4_SPV} ${H264_IDCT8_SPV} ${H264_QPEL_MC20_SPV})
 
     # v3d_runner — reusable Vulkan plumbing.
     add_library(v3d_runner STATIC src/v3d_runner.c)
@@ -450,6 +461,7 @@ if (DAEDALUS_BUILD_VULKAN)
         ${LPF8_SPV}
         ${CDEF_SPV}
         ${H264DEBLOCK_SPV}
+        ${H264DEBLOCK_H_SPV}
         ${H264_IDCT4_SPV}
         ${H264_IDCT8_SPV}
         ${H264_QPEL_MC20_SPV}