Phase 7: rename SkyOS → OrionOS across entire codebase

- Rename all binaries: skywm→orionwm, skydeskbar→oriondeskbar,
  skylauncher→orionlauncher, skyinstall/skyinstall-gui→orioninstall*
- Rename theme directory: themes/SkyOS/ → themes/OrionOS/
- Update all string literals, window titles, menu labels, and comments
- Update ISO build: hostname→orionos, user→orion, all paths/labels
- Add Plymouth boot splash theme (orionos) with Navy+Blue palette
- Update GTK2/GTK3 theme names, wallpaper output name
- Update .gitignore, root Makefile, build-iso.sh for new binary names

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

build-iso.sh

@@ -1,15 +1,15 @@
 #!/usr/bin/env bash
-# SkyOS ISO builder — run this on your Mac to produce a bootable ISO.
+# OrionOS ISO builder — run this on your Mac to produce a bootable ISO.
 # Requires: Docker Desktop (https://docker.com/products/docker-desktop)
 #
 # Usage: ./build-iso.sh
-# Output: dist/skyos-<date>.iso
+# Output: dist/orionos-<date>.iso
 set -euo pipefail
 
 REPO="$(cd "$(dirname "$0")" && pwd)"
 DIST="$REPO/dist"
-IMAGE="skyos-builder"
-ISO_TAG="skyos-$(date +%Y%m%d)"
+IMAGE="orionos-builder"
+ISO_TAG="orionos-$(date +%Y%m%d)"
 
 # ── preflight ─────────────────────────────────────────────────────────
 if ! command -v docker &>/dev/null; then
@@ -33,7 +33,7 @@ fi
 
 echo ""
 echo "┌─────────────────────────────────────────────┐"
-echo "│          SkyOS ISO Builder                  │"
+echo "│          OrionOS ISO Builder                  │"
 echo "│  Building a BeOS-inspired Linux desktop...  │"
 echo "└─────────────────────────────────────────────┘"
 echo ""
@@ -66,7 +66,7 @@ docker run \
 # ── rename with date tag ──────────────────────────────────────────────
 echo ""
 echo "Step 3/3: Finalizing..."
-ISO="$(find "$DIST" -name "skyos*.iso" | head -1)"
+ISO="$(find "$DIST" -name "orionos*.iso" | head -1)"
 if [[ -z "$ISO" ]]; then
     echo "ERROR: ISO not found in $DIST — check the build output above."
     exit 1