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/docker/Dockerfile

@@ -1,10 +1,10 @@
-# SkyOS ISO builder
+# OrionOS ISO builder
 # Uses official Arch Linux as the base — provides pacman, pacstrap, archiso.
 # Build context: the repo root (OS/)
 #
-# Build:  docker build -t skyos-builder -f iso/docker/Dockerfile .
-# Run:    docker run --privileged -v $(pwd)/dist:/dist skyos-builder
-# Output: dist/skyos.iso
+# Build:  docker build -t orionos-builder -f iso/docker/Dockerfile .
+# Run:    docker run --privileged -v $(pwd)/dist:/dist orionos-builder
+# Output: dist/orionos.iso
 
 FROM archlinux:latest
 
@@ -41,11 +41,11 @@ RUN su builder -c " \
 RUN echo "=== archiso initcpio hooks ===" && \
     ls /usr/lib/initcpio/hooks/ 2>/dev/null || echo "(none found)"
 
-# ── copy the entire SkyOS source tree ────────────────────────────────
-WORKDIR /skyos
+# ── copy the entire OrionOS source tree ──────────────────────────────
+WORKDIR /orionos
 COPY . .
 
-# ── build the SkyOS binaries inside the container ────────────────────
+# ── build the OrionOS binaries inside the container ───────────────────
 # pkg-config finds X11/Xft headers automatically on Arch — no overrides needed
 RUN make
 
@@ -54,4 +54,4 @@ RUN bash themes/wallpapers/generate-default.sh || true
 
 # ── run the ISO build script ──────────────────────────────────────────
 # --privileged is required for loop device mounts inside the container
-ENTRYPOINT ["/skyos/iso/docker/entrypoint.sh"]
+ENTRYPOINT ["/orionos/iso/docker/entrypoint.sh"]