Fix installer copy step; fix stale skyinstall references

Installer copy (installer/orioninstall):
- Root cause: rsync -ax / /mnt/ copies the overlayfs live root, which
  is slow, unpredictable, and hangs in VMs with overlapping filesystems
- Fix: copy from /run/archiso/airootfs instead (the squashfs is already
  mounted there on every archiso live boot). This is the clean base system,
  avoids the cow layer entirely, and is significantly faster.
- Added -H -A -X -S flags for proper hard-link, ACL, xattr, sparse-file handling
- Fallback to live-root rsync if the squashfs mount isn't present
- Also renamed EFI partition label SKYEFI → ORIONEFI

Discoverability (deskbar + wm):
- deskbar "Install OrionOS" was calling 'sudo skyinstall' (old name) — fixed
  to 'sudo orioninstall-gui || sudo orioninstall' with GUI-first fallback
- Right-click desktop menu now also has "Install OrionOS" entry
  (was only in the deskbar hamburger menu before)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wm/src/menu.c

@@ -18,6 +18,7 @@ static const MenuItem MENU_ITEMS[] = {
     { "Display Settings",  "arandr &"                                   },
     { "──────────────────", NULL                                         },
     { "Change Wallpaper",  "orionwallpaper --reset &"                    },
+    { "Install OrionOS",   "alacritty -e bash -c 'sudo orioninstall-gui 2>/dev/null || sudo orioninstall; exec bash' &" },
     { "──────────────────", NULL                                         },
     { "Restart OrionWM",   "pkill orionwm; sleep 0.2; orionwm &"        },
     { "Quit OrionOS",      "pkill orionwm"                              },