fix: add config.txt and DTBs to RPi boot control partition

The Raspberry Pi firmware reads config.txt from partition 1 BEFORE
processing autoboot.txt. Without arm_64bit=1 on the boot control
partition, the firmware defaults to 32-bit mode and shows only a
rainbow square. Add minimal config.txt, device tree blobs, and
overlays to partition 1 so the firmware can initialize correctly
before redirecting to the A/B boot partitions.

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

build/scripts/create-rpi-image.sh

@@ -161,6 +161,15 @@ boot_partition=2
 boot_partition=3
 AUTOBOOT
 
+# Minimal config.txt on partition 1 — firmware reads this BEFORE autoboot.txt
+# to determine arm_64bit mode and GPU settings. Without arm_64bit=1 here,
+# the firmware defaults to 32-bit and can't load our 64-bit kernel.
+cat > "$MNT_CTL/config.txt" << 'CFGTXT'
+arm_64bit=1
+enable_uart=1
+gpu_mem=16
+CFGTXT
+
 # Copy firmware blobs — REQUIRED on partition 1 for EEPROM to boot
 if ls "$RPI_FIRMWARE_DIR"/start*.elf 1>/dev/null 2>&1; then
     cp "$RPI_FIRMWARE_DIR"/start*.elf "$MNT_CTL/"
@@ -172,6 +181,14 @@ if [ -f "$RPI_FIRMWARE_DIR/bootcode.bin" ]; then
     cp "$RPI_FIRMWARE_DIR/bootcode.bin" "$MNT_CTL/"
 fi
 
+# Copy DTBs to partition 1 — firmware may need them before redirecting
+if ls "$RPI_FIRMWARE_DIR"/bcm27*.dtb 1>/dev/null 2>&1; then
+    cp "$RPI_FIRMWARE_DIR"/bcm27*.dtb "$MNT_CTL/"
+fi
+if [ -d "$RPI_FIRMWARE_DIR/overlays" ]; then
+    cp -r "$RPI_FIRMWARE_DIR/overlays" "$MNT_CTL/"
+fi
+
 # --- Helper: populate a boot partition ---
 populate_boot_partition() {
     local MNT="$1"