ffmpeg-v4l2-request-fourier: substitute H.264 IDCT 8×8 → daedalus-fourier

Cycle 7 of the libavcodec.so substitution arc (reauktion/daedalus-v4l2#11
step 2).  H264DSPContext.idct8_add — called per 8×8 block from the
High-profile intra-8×8-DCT decode path in libavcodec/h264_mb.c — now
dispatches through daedalus_recipe_dispatch_h264_idct8 instead of
ff_h264_idct8_add_neon.

## What

- Add 0004-h264-idct8-daedalus-fourier.patch (in both arch/ and debian/
  ffmpeg-v4l2-request-fourier/).  Extends libavcodec/aarch64/
  h264_idct_daedalus.c (introduced by 0003) with ff_h264_idct8_add_daedalus
  and a daedalus_recipe_dispatch_h264_idct8 call; patches
  libavcodec/aarch64/h264dsp_init_aarch64.c to wire c->idct8_add to
  the new shim.
- arch/PKGBUILD + debian/build-deb.sh: append the new patch to the
  apply list; bump pkgrel/PKGREL to 7.
- No new build-deps, no Depends change, no daedalus-fourier rev — the
  d87239d pin already exposes daedalus_recipe_dispatch_h264_idct8.

## Why

The recipe layer picks the substrate; for cycle 7 (H.264 IDCT 8×8)
the recipe is CPU NEON, so this is effectively a NEON-to-NEON
substitution layered on top of cycle 6.  Production validation of
cycle 6 on higgs Firefox YouTube: 3040 frames decoded cleanly,
avg_decode_us=3388 (no regression vs the pre-substitution ~4 ms
baseline).  Cycle 7 inherits the same shim's pthread_once context.

Bit-exact against ff_h264_idct8_add_neon (daedalus-fourier cycle 7
green; FFmpeg 8×8 block storage block[r + 8*c] matches daedalus
column-major convention).

## Scope NOT covered (deferred)

- Bulk c->idct8_add4 (inter 8×8-DCT macroblocks) stays on the
  in-tree NEON .S code; batched substitution with n_blocks>1 lands
  later alongside the cycle-6 bulk-paths work.
- High-bit-depth (10-bit) path untouched.
- Cycles 8/9 — separate PRs.

## SONAME

Unchanged.  libavcodec.so.62 / libavformat.so.62 / libavutil.so.60.

## Refs

- reauktion/daedalus-v4l2 issue #11 (substitution arc): reauktion/daedalus-v4l2#11
- marfrit-packages PR #76 (cycle 6 IDCT 4×4)
- marfrit-packages PR #78 (libxml2 ABI-skew workaround)
- marfrit/daedalus-fourier cycle 7 close (H.264 IDCT 8×8 NEON green)

arch/ffmpeg-v4l2-request-fourier/PKGBUILD

@@ -24,7 +24,7 @@ _srcname=FFmpeg
 _version='8.1'
 _commit='b57fbbe50c9b2656fad86a1a7eeabfd2b2a50935'  # v4l2-request-n8.1 tip 2026-04-24
 pkgver=8.1.r123329.b57fbbe
-pkgrel=6   # pkgrel=6 — H.264 IDCT 4x4 daedalus-fourier substitution (2026-05-21)
+pkgrel=7   # pkgrel=7 — H.264 IDCT 8x8 daedalus-fourier substitution (cycle 7, 2026-05-22)
 epoch=2
 
 # daedalus-fourier pin — first kernel substitution in libavcodec
@@ -90,8 +90,9 @@ source=("git+https://github.com/Kwiboo/FFmpeg.git#commit=${_commit}"
         "daedalus-fourier-${_daedalus_fourier_commit}.tar.gz::https://git.reauktion.de/marfrit/daedalus-fourier/archive/${_daedalus_fourier_commit}.tar.gz"
         '0001-libudev-bypass-fallback.patch'
         '0002-nv15-to-p010-unpack.patch'
-        '0003-h264-idct4-daedalus-fourier.patch')
-sha256sums=('SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP')
+        '0003-h264-idct4-daedalus-fourier.patch'
+        '0004-h264-idct8-daedalus-fourier.patch')
+sha256sums=('SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP')
 
 pkgver() {
   cd "${_srcname}"
@@ -105,6 +106,7 @@ prepare() {
   patch -Np1 -i "${srcdir}/0001-libudev-bypass-fallback.patch"
   patch -Np1 -i "${srcdir}/0002-nv15-to-p010-unpack.patch"
   patch -Np1 -i "${srcdir}/0003-h264-idct4-daedalus-fourier.patch"
+  patch -Np1 -i "${srcdir}/0004-h264-idct8-daedalus-fourier.patch"
 }
 
 build() {