ffmpeg-v4l2-request-fourier: substitute H.264 luma-v deblock → daedalus-fourier

Cycle 8 of the libavcodec.so substitution arc (reauktion/daedalus-v4l2#11
step 2).  H264DSPContext.v_loop_filter_luma — non-intra bS<4 vertical
luma deblock, called per macroblock-row edge from the slice deblock
loop in libavcodec/h264_loopfilter.c — now dispatches through
daedalus_recipe_dispatch_h264_deblock_luma_v instead of
ff_h264_v_loop_filter_luma_neon.

## What

- Add 0005-h264-deblock-luma-v-daedalus-fourier.patch (in both arch/
  and debian/ ffmpeg-v4l2-request-fourier/).  Extends
  libavcodec/aarch64/h264_idct_daedalus.c with
  ff_h264_v_loop_filter_luma_daedalus (constructs a
  daedalus_h264_deblock_meta from FFmpeg's (alpha, beta, tc0[4]) and
  calls daedalus_recipe_dispatch_h264_deblock_luma_v with n_edges=1).
  Patches libavcodec/aarch64/h264dsp_init_aarch64.c to wire
  c->v_loop_filter_luma to the new shim.
- arch/PKGBUILD + debian/build-deb.sh: append patch + bump pkgrel/PKGREL
  to 8.
- No new build-deps, no Depends change, no daedalus-fourier rev — the
  d87239d pin already exposes daedalus_recipe_dispatch_h264_deblock_luma_v.

## Why

Cycle 8 is marked "CPU primary; QPU opportunistic" in the daedalus-
fourier API docstring.  Per the hybrid substrate philosophy
("if there's a coprocessor, use it") we eventually want the QPU
opportunism active here.  But the libavcodec.so context is
process-global and shared with cycles 6/7 via pthread_once, and it
uses daedalus_ctx_create_no_qpu deliberately to avoid implicit
Vulkan init in arbitrary host processes (Firefox content, mpv-fourier,
ffmpeg-fourier CLI, ...).  Switching to daedalus_ctx_create here
without a feature flag would be a footgun.

So cycle 8 lands as plumbing-only NEON-by-recipe substitution for
now; opportunistic QPU enablement is a separate follow-up that adds
a DAEDALUS_FOURIER_ENABLE_QPU env var or equivalent.

## Scope NOT covered

- Intra (bS=4) loop filter c->v_loop_filter_luma_intra — daedalus's
  daedalus_h264_deblock_meta only covers the non-intra path.
- Horizontal-edge variant c->h_loop_filter_luma — separate kernel
  (not yet in daedalus-fourier API).
- Chroma loop filters — separate kernels.
- Bulk batching — single-edge dispatch wastes the kernel's n_edges>1
  amortization.  Same caveat as cycles 6/7; follow-up.
- QPU opportunism — see "Why" above.

## SONAME

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

## Refs

- reauktion/daedalus-v4l2 issue #11: reauktion/daedalus-v4l2#11
- marfrit-packages PR #76 (cycle 6 IDCT 4×4)
- marfrit-packages PR #85 (cycle 7 IDCT 8×8)
- marfrit/daedalus-fourier cycle 8 close (deblock luma-v 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=7   # pkgrel=7 — H.264 IDCT 8x8 daedalus-fourier substitution (cycle 7, 2026-05-22)
+pkgrel=8   # pkgrel=8 — H.264 luma-v deblock daedalus-fourier substitution (cycle 8, 2026-05-22)
 epoch=2
 
 # daedalus-fourier pin — first kernel substitution in libavcodec
@@ -91,8 +91,9 @@ source=("git+https://github.com/Kwiboo/FFmpeg.git#commit=${_commit}"
         '0001-libudev-bypass-fallback.patch'
         '0002-nv15-to-p010-unpack.patch'
         '0003-h264-idct4-daedalus-fourier.patch'
-        '0004-h264-idct8-daedalus-fourier.patch')
-sha256sums=('SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP')
+        '0004-h264-idct8-daedalus-fourier.patch'
+        '0005-h264-deblock-luma-v-daedalus-fourier.patch')
+sha256sums=('SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP' 'SKIP')
 
 pkgver() {
   cd "${_srcname}"
@@ -107,6 +108,7 @@ prepare() {
   patch -Np1 -i "${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"
+  patch -Np1 -i "${srcdir}/0005-h264-deblock-luma-v-daedalus-fourier.patch"
 }
 
 build() {