fix: Restructure containers - aios contains child containers internally

Changed from 3 separate containers to 1 container with child containers inside:
- /var/lib/machines/aios/ (main container)
  - /var/lib/machines/restore-img/ (child container)
  - /var/lib/machines/workspace/ (child container)

ai user operates child containers from within aios using machinectl.

cfg/aios-ctl.zsh

@@ -21,9 +21,9 @@ function aios-shell() {
     sudo machinectl shell $NAME
 }
 
-# Login to aios container
+# Login to aios container as ai user
 function aios-login() {
-    sudo machinectl login $NAME
+    sudo machinectl shell $NAME /bin/su - ai
 }
 
 # Create backup of current aios