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>

init/lib/20-persistent-mount.sh

@@ -58,11 +58,33 @@ esac
 
 if [ ! -b "$KUBESOLO_DATA_DEV" ]; then
     log_err "Data device $KUBESOLO_DATA_DEV not found after ${WAIT_SECS}s"
-    # Show available block devices for debugging
-    log_err "Available block devices:"
-    ls -la /dev/mmc* /dev/sd* /dev/vd* 2>/dev/null | while read -r line; do
+    # Comprehensive diagnostics for block device failure
+    log_err "=== Block device diagnostics ==="
+    log_err "--- /dev block devices ---"
+    ls -la /dev/mmc* /dev/sd* /dev/vd* /dev/nvme* 2>/dev/null | while read -r line; do
         log_err "  $line"
     done
+    log_err "--- /sys/class/block (kernel registered) ---"
+    ls /sys/class/block/ 2>/dev/null | while read -r line; do
+        log_err "  $line"
+    done
+    log_err "--- dmesg: MMC/SDHCI/emmc ---"
+    dmesg 2>/dev/null | grep -i -e mmc -e sdhci -e emmc | while read -r line; do
+        log_err "  $line"
+    done
+    log_err "--- dmesg: regulator ---"
+    dmesg 2>/dev/null | grep -i regulator | while read -r line; do
+        log_err "  $line"
+    done
+    log_err "--- dmesg: firmware/mailbox ---"
+    dmesg 2>/dev/null | grep -i -e 'raspberrypi' -e 'mailbox' -e 'firmware' | while read -r line; do
+        log_err "  $line"
+    done
+    log_err "--- dmesg: errors ---"
+    dmesg 2>/dev/null | grep -i -e 'error' -e 'fail' -e 'unable' | while read -r line; do
+        log_err "  $line"
+    done
+    log_err "=== End diagnostics ==="
     return 1
 fi