add mpv-fourier scaffold (delivery vehicle for dmabuf-modifier-triage iter1)

mpv on ohm is currently stock arch from [extra]. To ship the
vo_dmabuf_wayland plane-semantics fix per
marfrit/dmabuf-modifier-triage#1, we need an mpv-fourier package
following the same fourier-umbrella pattern as kwin-fourier,
qt6-base-fourier, firefox-fourier, libva-v4l2-request-fourier.

This commit lays down:

- arch/mpv-fourier/PKGBUILD pinning upstream mpv 0.41.0 tarball, with
  empty patch slot in prepare(). replaces=mpv. provides=mpv,libmpv.so.
  When iter1 produces the patch, add it to source=()/sha256sums=()
  and uncomment the patch -p1 line.
- arch/mpv-fourier/README.md documenting why + tracker links
- .gitea/workflows/build.yml job mpv-fourier-aarch64 chained after
  libva-v4l2-request-fourier-aarch64 for marfrit.db serialization.
  Same fermi LXC runner, same makepkg → sign → repo-add → rsync flow.

Initial scaffold builds vanilla mpv 0.41.0 with no fourier patches —
once iter1 lands, bump pkgrel and add the patch.

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

arch/mpv-fourier/PKGBUILD

@@ -0,0 +1,134 @@
+# Maintainer: Markus Fritsche <fritsche.markus@gmail.com>
+#
+# mpv-fourier — mpv with the fourier-umbrella patches. The first patch
+# slot exists for the vo_dmabuf_wayland plane-semantics fix per
+# marfrit/dmabuf-modifier-triage#1: mpv currently constructs the
+# zwp_linux_buffer_params_v1 wl_protocol message with internally
+# inconsistent plane semantics on V4L2 stateless decoder dmabufs (per-
+# plane fds combined with single-allocation offset for plane 1), causing
+# KWin to read the UV chroma plane past-EOF and render solid dark green
+# on ohm (RK3566 + hantro G1 + Mali-G52). The patch is not yet written —
+# this scaffold prepares the shipping path for when iter1 lands.
+#
+# Campaign: ~/src/dmabuf-modifier-triage/ (Phase 0 closed 2026-05-08)
+# Upstream: https://github.com/mpv-player/mpv
+# Build target: fermi LXC actrunner-aarch64-hertz via marfrit-packages
+# Gitea Actions; alternative: boltzmann via his subagent + marfrit-publish.
+
+pkgname=mpv-fourier
+_upstreampkg=mpv
+pkgver=0.41.0
+pkgrel=1
+pkgdesc='mpv with fourier-umbrella patches (vo_dmabuf_wayland plane-semantics fix slot)'
+arch=('aarch64')
+url='https://mpv.io/'
+license=('GPL-2.0-or-later' 'LGPL-2.1-or-later')
+depends=(
+    alsa-lib
+    desktop-file-utils
+    ffmpeg
+    glibc
+    hicolor-icon-theme
+    jack
+    lcms2
+    libarchive
+    libass
+    libbluray
+    libcdio
+    libcdio-paranoia
+    libdisplay-info
+    libdrm
+    libdvdnav
+    libdvdread
+    libegl
+    libgl
+    libglvnd
+    libjpeg-turbo
+    libplacebo
+    libpulse
+    libsixel
+    libva
+    libvdpau
+    libx11
+    libxext
+    libxkbcommon
+    libxpresent
+    libxrandr
+    libxss
+    libxv
+    luajit
+    mesa
+    mujs
+    libpipewire
+    rubberband
+    sdl2
+    openal
+    uchardet
+    vapoursynth
+    vulkan-icd-loader
+    wayland
+    zlib
+)
+makedepends=(
+    git
+    meson
+    ninja
+    pkgconf
+    python-docutils
+    wayland-protocols
+)
+optdepends=(
+    'yt-dlp: for video-sharing websites playback'
+)
+provides=("${_upstreampkg}=${pkgver}" 'libmpv.so')
+conflicts=("${_upstreampkg}")
+replaces=("${_upstreampkg}")
+
+source=(
+    "${_upstreampkg}-${pkgver}.tar.gz::https://github.com/mpv-player/${_upstreampkg}/archive/v${pkgver}/${_upstreampkg}-${pkgver}.tar.gz"
+)
+sha256sums=(
+    'ee21092a5ee427353392360929dc64645c54479aefdb5babc5cfbb5fad626209'
+)
+
+prepare() {
+    cd "${_upstreampkg}-${pkgver}"
+
+    # Patch slot — iter1 of dmabuf-modifier-triage will produce the actual
+    # vo_dmabuf_wayland.c plane-semantics fix and add it as 0001-... here.
+    # Once the libva path is also unblocked (by libva-multiplanar iter9)
+    # and the WAYLAND_DEBUG verifier confirms whether the bug is purely in
+    # mpv's VO or also in libva/ffmpeg producer code, the exact patch
+    # shape is determined.
+    #
+    # When the patch lands, add it to source=() above + sha256sums=() and
+    # uncomment the patch -p1 below.
+    #
+    # patch -p1 < "${srcdir}/0001-vo_dmabuf_wayland-plane-semantics.patch"
+    :
+}
+
+build() {
+    cd "${_upstreampkg}-${pkgver}"
+    arch-meson build \
+        --buildtype=release \
+        -Dlibmpv=true \
+        -Dmanpage-build=enabled \
+        -Dcdda=enabled \
+        -Ddvbin=enabled \
+        -Ddvdnav=enabled \
+        -Dlibarchive=enabled \
+        -Dopenal=enabled \
+        -Dsdl2-audio=enabled \
+        -Dsdl2-video=enabled \
+        -Dsdl2-gamepad=enabled
+    meson compile -C build
+}
+
+package() {
+    cd "${_upstreampkg}-${pkgver}"
+    meson install -C build --destdir "${pkgdir}"
+
+    install -Dm644 LICENSE.GPL  "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE.GPL"
+    install -Dm644 LICENSE.LGPL "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE.LGPL"
+}