fix: resolve DRI driver deps + set Mesa env vars for SDL3/GBM

- docker-build.sh: transitive dep loop now includes lib64/dri/*.so
(DRI drivers have many deps that were never resolved)
- init: set LD_LIBRARY_PATH, LIBGL_DRIVERS_PATH, GBM_DRIVERS_PATH,
MESA_LOADER_DRIVER_OVERRIDE=iris for Intel UHD 615
- AC_BUILD_SDL now defaults to 0; this fix prepares for re-enabling

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

fedac/native/docker-build.sh

···
 ADDED=1
 while [ "$ADDED" -gt 0 ]; do
     ADDED=0
-    for elf in "$IROOT/lib64/"*.so* "$IROOT/ac-native"; do
+    for elf in "$IROOT/lib64/"*.so* "$IROOT/lib64/dri/"*.so* "$IROOT/ac-native"; do
         [ -f "$elf" ] || continue
         for needed in $(readelf -d "$elf" 2>/dev/null | grep NEEDED | sed 's/.*\[\(.*\)\]/\1/'); do
             if [ ! -f "$IROOT/lib64/$needed" ]; then

fedac/native/initramfs/init

···
 # Main loop — restart on crash, poweroff on exit 0, reboot on exit 2
 CRASH_COUNT=0
 while true; do
-    /ac-native /piece.mjs 2>/tmp/ac-native-stderr.log
+    LD_LIBRARY_PATH="/lib64" LIBGL_DRIVERS_PATH="/lib64/dri" GBM_DRIVERS_PATH="/lib64/dri" MESA_LOADER_DRIVER_OVERRIDE=iris /ac-native /piece.mjs 2>/tmp/ac-native-stderr.log
     EXIT_CODE=$?
     echo "[init] ac-native exited: code=$EXIT_CODE crash=$CRASH_COUNT" > /dev/tty0 2>/dev/null
     echo "[init] stderr: $(tail -5 /tmp/ac-native-stderr.log 2>/dev/null)" > /dev/tty0 2>/dev/null