fix: Correct OS structure - root.x86_64 is OS root, not machines/aios

Fixed the fundamental issue:
- root.x86_64/ = aios OS (entire filesystem)
- root.x86_64/var/lib/machines/ = child containers directory

Changes:
- build.zsh: Use root.x86_64 directly as OS root
- setup-user.sh: ROOTFS=root.x86_64
- setup-claude.sh: ROOTFS=root.x86_64
- user-continer.sh: ROOTFS=root.x86_64
- install.sh: mv root.x86_64 /var/lib/machines/aios

Now matches github-actions structure correctly.

cfg/setup-user.sh

@@ -2,7 +2,7 @@
 # User setup for aios
 # Creates ai user, configures auto-login, sudo, zshrc
 
-ROOTFS="root.x86_64/var/lib/machines/aios"
+ROOTFS="root.x86_64"
 
 echo "=== User Setup ==="