Phase 8a: H.264 kernels through public API

Extends include/daedalus.h with cycles 6, 7, 8 (H.264 IDCT 4x4,
IDCT 8x8, luma deblock luma-v). All recipe-substrate = CPU
(matches per-cycle Phase 7 verdicts).

src/daedalus_core.c: NEON-path implementations + recipe routing.
daedalus_core library now links the full FFmpeg H.264 NEON
snapshot (h264idct + h264dsp) plus existing VP9 + dav1d.

tests/test_api_h264.c: smoke test covering all 3 H.264 kernels
via daedalus_recipe_dispatch_*. All pass 2048/2048 bit-exact.

Public API coverage after this commit:
- Cycles 1 IDCT 8x8 + 2 LPF4 + 4 LPF8: CPU+QPU+AUTO dispatch
  (test_api_idct, test_api_lpf, both pass)
- Cycle 3 MC 8h: CPU only (QPU dispatch stub returns -1)
- Cycle 5 CDEF: CPU only (QPU stub)
- Cycle 6 H.264 IDCT 4x4: CPU only (recipe + only NEON wired)
- Cycle 7 H.264 IDCT 8x8: CPU only
- Cycle 8 H.264 deblock: CPU only (QPU opportunistic — not wired
  through API yet; bench_v3d_h264deblock exists for direct test)

Next Phase 8 sub-step: wire opportunistic QPU dispatch for cycles
3+5+8 through the API (so override-mode users can request QPU).
Then surface V4L2-wrapper architecture decisions to user.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -347,6 +347,8 @@ add_library(daedalus_core STATIC
     ${FFASM_LPF_SOURCES}
     ${FFASM_MC_SOURCES}
     ${FFC_MC_SOURCES}
+    ${FFASM_H264IDCT_SOURCES}
+    ${FFASM_H264DSP_SOURCES}
     ${DAV1D_CDEF_ASM_SOURCES}
     ${DAV1D_CDEF_C_SOURCES}
 )
@@ -373,6 +375,15 @@ add_executable(test_api_lpf
 target_link_libraries(test_api_lpf PRIVATE daedalus_core)
 target_compile_options(test_api_lpf PRIVATE -O2)
 
+add_executable(test_api_h264
+    tests/test_api_h264.c
+    tests/h264_idct4_ref.c
+    tests/h264_idct8_ref.c
+    tests/h264_deblock_ref.c
+)
+target_link_libraries(test_api_h264 PRIVATE daedalus_core)
+target_compile_options(test_api_h264 PRIVATE -O2)
+
 if (DAEDALUS_BUILD_VULKAN)
 # (re-open the conditional so the closing endif() below balances)