rpi: add boot diagnostics and remove quiet for debugging

Remove 'quiet' from RPi cmdline.txt so kernel probe messages are
visible on HDMI. Add comprehensive diagnostics to the data device
error path: dmesg for MMC/SDHCI/regulators/firmware, /sys/class/block
listing, and error message scanning. This will reveal why zero block
devices appear despite all kernel configs being correct.

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

build/scripts/create-rpi-image.sh

@@ -173,7 +173,7 @@ CFGTXT
 
     # cmdline.txt — kernel command line
     # Note: must be a single line
-    echo "console=serial0,115200 console=tty1 kubesolo.data=LABEL=KSOLODATA quiet" > "$MNT/cmdline.txt"
+    echo "console=serial0,115200 console=tty1 kubesolo.data=LABEL=KSOLODATA" > "$MNT/cmdline.txt"
 
     # Copy kernel as kernel8.img (RPi 3/4/5 ARM64 convention)
     cp "$KERNEL" "$MNT/kernel8.img"