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>

installer/orioninstall

@@ -141,7 +141,7 @@ ok "Partitioned."
 progress 10 "Formatting partitions…"
 info "Formatting..."
 if [[ "$BOOT_MODE" == "uefi" ]]; then
-    mkfs.fat -F32 -n SKYEFI "$EFI_PART"
+    mkfs.fat -F32 -n ORIONEFI "$EFI_PART"
     ok "EFI: FAT32 ($EFI_PART)"
 fi
 mkfs.ext4 -L OrionOS "$ROOT_PART"
@@ -160,9 +160,28 @@ ok "Mounted."
 # ── 4. Copy live system ───────────────────────────────────────────────
 progress 18 "Copying live system (this takes a few minutes)…"
 info "Copying live system to disk..."
-rsync -ax \
-    --exclude={/proc,/sys,/dev,/run,/mnt,/media,/tmp,/lost+found} \
-    / /mnt/
+
+# On archiso live systems the squashfs is already mounted at
+# /run/archiso/airootfs. Copy from there: it's the clean base system
+# (no live-session overlay junk) and it's much faster and more reliable
+# than rsyncing the overlayfs root.
+SFS_ROOT="/run/archiso/airootfs"
+if [[ -d "$SFS_ROOT" ]] && [[ -f "$SFS_ROOT/etc/os-release" ]]; then
+    info "Copying from squashfs mount at $SFS_ROOT..."
+    rsync -axHAXS "$SFS_ROOT/" /mnt/
+else
+    info "Squashfs not found; falling back to live root copy..."
+    rsync -axHAXS \
+        --exclude=/proc/ \
+        --exclude=/sys/ \
+        --exclude=/dev/ \
+        --exclude=/run/ \
+        --exclude=/mnt/ \
+        --exclude=/media/ \
+        --exclude=/tmp/ \
+        --exclude=/lost+found \
+        / /mnt/
+fi
 ok "Files copied."
 
 # ── 5. fstab ─────────────────────────────────────────────────────────