ix init script duplication and CPIO creation issues

- Remove duplicate /sbin/init copying from initramfs_setup_zinit()
- Only /init should be config/init (initramfs setup script)
- No /sbin/init needed - config/init calls 'switch_root /mnt/root /sbin/zinit init'
- Remove unsupported cpio --owner option that broke CPIO creation
- Fix validation to not expect /sbin/init file
- Correct boot flow: /init → switch_root → /sbin/zinit init
- Remove strip and UPX compression from zinit binary copying
- UPX compression was corrupting the zinit binary causing segfaults after switch_root
- Keep zinit unmodified as it's

.build-stages/cleanup.done

@@ -0,0 +1,5 @@
+# Stage completion marker
+STAGE_NAME="cleanup"
+COMPLETED_AT="2025-09-05T09:35:22+00:00"
+COMPLETED_BY="root"
+DETAILS="Duration: 0s, Function: stage_cleanup"