rpi: drop to interactive shell on boot failure, add initcall_debug

Instead of returning 1 (which triggers kernel panic via set -e before
emergency_shell runs), exec an interactive shell on /dev/console so
the user can run dmesg and debug interactively. Add initcall_debug
and loglevel=7 to cmdline.txt to show every driver probe during boot.
Also dump last 60 lines of dmesg before dropping to shell.

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

init/lib/20-persistent-mount.sh

@@ -84,8 +84,20 @@ if [ ! -b "$KUBESOLO_DATA_DEV" ]; then
     dmesg 2>/dev/null | grep -i -e 'error' -e 'fail' -e 'unable' | while read -r line; do
         log_err "  $line"
     done
+    log_err "--- Full dmesg (last 60 lines) ---"
+    dmesg 2>/dev/null | tail -60 | while read -r line; do
+        log_err "  $line"
+    done
     log_err "=== End diagnostics ==="
-    return 1
+    log_err ""
+    log_err "Dropping to debug shell in 10 seconds..."
+    log_err "Run 'dmesg' to see full kernel log."
+    log_err "Run 'ls /sys/class/block/' to check block devices."
+    log_err ""
+    sleep 10
+    # Drop to interactive shell instead of returning failure
+    # (returning 1 with set -e causes kernel panic before emergency_shell)
+    exec /bin/sh </dev/console >/dev/console 2>&1
 fi
 
 # Mount data partition (format on first boot if unformatted)