Fix remaining sky* references missed in Phase 7 rename

- Dockerfile: WORKDIR /skyos → /orionos, ENTRYPOINT path, image name
- Makefile: skyos-default.png → orionos-default.png in install target
- iso/build-base.sh: all sky*/SkyOS → orion*/OrionOS
- iso/mac-install-notes.md: update install instructions for OrionOS
- themes/OrionOS: finish renaming sky* strings in gtkrc, gtk.css, index.theme

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

iso/mac-install-notes.md

@@ -1,17 +1,17 @@
-# Installing SkyOS on an Intel Mac
+# Installing OrionOS on an Intel Mac
 
 ## Before you start
 
 - Intel Mac (any MacBook/MacBook Pro with Intel CPU — 2006–2020)
 - USB drive ≥ 4 GB
-- The SkyOS ISO
+- The OrionOS ISO
 
 ## Step 1 — Boot from USB
 
 Intel Macs use EFI + rEFInd (included in the ISO) to boot Linux.
 
 1. Hold **Option (⌥)** at startup to see the boot picker.
-2. Select the SkyOS USB drive (shows as "EFI Boot").
+2. Select the OrionOS USB drive (shows as "EFI Boot").
 
 ## Step 2 — Partition the disk
 
@@ -27,7 +27,7 @@ Format:
 ```bash
 mkfs.fat -F32 /dev/sda1
 mkswap /dev/sda2
-mkfs.ext4 -L SkyOS /dev/sda3
+mkfs.ext4 -L OrionOS /dev/sda3
 ```
 
 ## Step 3 — Install
@@ -56,7 +56,7 @@ points it at the right initramfs.
 
 ## Step 5 — First boot
 
-Log in as `sky` (password: `skyos` — change it!), then:
+Log in as `sky` (password: `orionos` — change it!), then:
 
 ```bash
 startx