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/install.sh

@@ -9,7 +9,7 @@ echo "=== aios installation ==="
 # Extract and install
 tar xf "$TARBALL"
 mkdir -p /var/lib/machines
-mv root.x86_64/var/lib/machines/aios /var/lib/machines/$NAME
+mv root.x86_64 /var/lib/machines/$NAME
 
 echo "=== Installation complete ==="
 echo ""