chromium-fourier: bump to 148.0.7778.178, add Debian recipe

Arch: version 147→148, drop enable_nacl (removed upstream), fix
nv12-external-oes patch context for 148 (base/numerics/safe_conversions.h
include removed upstream). Header comment updated: native build fiction →
cross-compile reality.

Debian: new build-deb.sh that assembles .deb from pre-built artifacts
on CT 220 (data). Same binary artifacts as the Arch package, launcher at
/usr/bin/chromium-fourier (no Conflicts with stock chromium on Debian).

Both packages published to packages.reauktion.de:
- Arch: marfrit/aarch64/chromium-fourier 1:148.0.7778.178-1
- Debian: trixie+bookworm/main/arm64 chromium-fourier 1:148.0.7778.178-1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

arch/chromium-fourier/patches/nv12-external-oes-on-modifier-external-only.patch

@@ -73,16 +73,15 @@ diff --git a/ui/ozone/common/native_pixmap_egl_binding.cc b/ui/ozone/common/nati
 index 31877f4459..6855c1093e 100644
 --- a/ui/ozone/common/native_pixmap_egl_binding.cc
 +++ b/ui/ozone/common/native_pixmap_egl_binding.cc
-@@ -6,10 +6,13 @@
- 
+@@ -6,9 +6,12 @@
+
  #include <array>
- 
+
 +#include "base/containers/flat_map.h"
  #include "base/logging.h"
  #include "base/memory/scoped_refptr.h"
 +#include "base/no_destructor.h"
  #include "base/notreached.h"
- #include "base/numerics/safe_conversions.h"
 +#include "base/synchronization/lock.h"
  #include "ui/gfx/linux/drm_util_linux.h"
  #include "ui/gl/gl_bindings.h"