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>

themes/OrionOS/gtk-2.0/gtkrc

@@ -1,4 +1,4 @@
-# SkyOS GTK2 Theme — dark navy palette (legacy GTK2 apps)
+# OrionOS GTK2 Theme — dark navy palette (legacy GTK2 apps)
 
 gtk-color-scheme = "bg_color:#1E2436\nfg_color:#D8E4F4\nbase_color:#0E1424\ntext_color:#D8E4F4\nselected_bg_color:#1E4D78\nselected_fg_color:#F0F6FF\ntooltip_bg_color:#0C1020\ntooltip_fg_color:#D8E4F4"
 
@@ -63,7 +63,7 @@ style "entry" {
 }
 class "GtkEntry" style "entry"
 
-gtk-theme-name        = "SkyOS"
+gtk-theme-name        = "OrionOS"
 gtk-icon-theme-name   = "Adwaita"
 gtk-font-name         = "Sans 10"
 gtk-cursor-theme-name = "DMZ-White"

themes/OrionOS/gtk-3.0/gtk.css

@@ -1,4 +1,4 @@
-/* SkyOS GTK3 Theme — dark navy palette matching skywm/skydeskbar */
+/* OrionOS GTK3 Theme — dark navy palette matching orionwm/oriondeskbar */
 
 @define-color bg_color       #1E2436;
 @define-color bg_dark        #161C2A;

themes/OrionOS/index.theme

@@ -1,12 +1,12 @@
 [Desktop Entry]
 Type=X-GNOME-Metatheme
-Name=SkyOS
-Comment=BeOS/SkyOS-inspired warm tan desktop theme
+Name=OrionOS
+Comment=BeOS/OrionOS-inspired warm tan desktop theme
 Encoding=UTF-8
 
 [X-GNOME-Metatheme]
-GtkTheme=SkyOS
-MetacityTheme=SkyOS
+GtkTheme=OrionOS
+MetacityTheme=OrionOS
 IconTheme=Adwaita
 CursorTheme=DMZ-White
 ButtonLayout=close:minimize,maximize