fix: install our staged init at /init too, not just /sbin/init

The kernel ALWAYS runs /init when booting from an initramfs. If /init doesn't
exist, the kernel falls back to the legacy root-mount path (looking for a real
root partition via root= cmdline), which we don't want — our system IS the
initramfs.

Previous fix removed piCore's /init to stop it from being run; that caused the
kernel to skip the initramfs entrypoint entirely and panic with 'Cannot open
root device' (error -6).

Correct fix: replace piCore's /init with a copy of our init.sh. The kernel
runs /init -> our staged boot, which is exactly what we want. Keep
/sbin/init as well (some boot paths exec it directly, e.g. via init= cmdline
override) and the existing init=/sbin/init in grub-arm64.cfg as a belt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

build/scripts/inject-kubesolo.sh

@@ -55,14 +55,14 @@ rm -f "$ROOTFS/sbin/init"
 cp "$PROJECT_ROOT/init/init.sh" "$ROOTFS/sbin/init"
 chmod +x "$ROOTFS/sbin/init"
 
-# Remove piCore/TC's /init at the rootfs root. The kernel's init search order
-# is /init -> /sbin/init -> ..., so leaving piCore's /init in place causes the
-# kernel to run that instead of ours, which then segfaults (it tries to do
-# piCore-specific TCE handling on a host that doesn't have it).
-if [ -e "$ROOTFS/init" ]; then
+# Replace the upstream /init at the rootfs root with our staged init.
+# The kernel ALWAYS runs /init when booting from an initramfs (legacy root-mount
+# fallback otherwise). piCore/TC ship their own /init; ours has to take its
+# place so the kernel runs our staged boot, not piCore's TCE handler.
 rm -f "$ROOTFS/init"
-    echo "    Removed upstream /init (kernel will fall through to /sbin/init)"
-fi
+cp "$PROJECT_ROOT/init/init.sh" "$ROOTFS/init"
+chmod +x "$ROOTFS/init"
+echo "    Installed staged init at /init and /sbin/init"
 
 # Init stages
 mkdir -p "$ROOTFS/usr/lib/kubesolo-os/init.d"