revert: keep kernel 6.19.9 — the boot issue is not kernel version

Co-Authored-By: Claude Opus 4.6 (1M context) <[e-mail]>

fedac/native/Dockerfile.builder

···
 RUN mkdir -p /cache && cd /cache \
     && curl -sL https://bellard.org/quickjs/quickjs-2024-01-13.tar.xz | tar xJ \
     && ln -sf quickjs-2024-01-13 quickjs \
-    && curl -sL https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.14.2.tar.xz | tar xJ \
-    && echo "=== Cached: QuickJS + Linux 6.14.2 ==="
+    && curl -sL https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.19.9.tar.xz | tar xJ \
+    && echo "=== Cached: QuickJS + Linux 6.19.9 ==="
 
 # ── Install esbuild for KidLisp bundling ──
 RUN npm install -g esbuild

fedac/native/docker-build.sh

···
 OUT="${AC_OUT:-/out}"
 NATIVE="$SRC/fedac/native"
 BUILD="$NATIVE/build"
-KVER="${KERNEL_VERSION:-6.14.2}"
+KVER="${KERNEL_VERSION:-6.19.9}"
 KMAJOR="${KVER%%.*}"
 MEDIA_LAYOUT_LIB="$NATIVE/scripts/media-layout.sh"