Add wallpaper rotation system with upgrade workflow

- Add home/wallpapers/default.nix with per-wallpaper scaling options
- Add 5 new Metroid-themed wallpapers to the rotation
- Update i3+sway and plasma-manager to use wallpaper module
- Add scripts/rotate-wallpaper.sh to cycle through wallpapers
- Add scripts/upgrade.sh to chain: flake update, doom, claude-code, wallpaper
- Add flake apps: rotate-wallpaper, update-claude-code, upgrade
- Fix claude-code update.sh to use REPO_ROOT for flake app compatibility

Run `nix run .#upgrade` for full system update with wallpaper rotation.

scripts/rotate-wallpaper.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+# Configuration
+REPO_ROOT="${REPO_ROOT:-$(git rev-parse --show-toplevel 2>/dev/null || pwd)}"
+WALLPAPER_FILE="$REPO_ROOT/home/wallpapers/default.nix"
+
+echo -e "${GREEN}Rotating wallpaper...${NC}"
+
+# Check if file exists
+if [[ ! -f "$WALLPAPER_FILE" ]]; then
+    echo -e "${RED}Error: $WALLPAPER_FILE not found${NC}"
+    exit 1
+fi
+
+# Get current index
+CURRENT_INDEX=$(grep -oP 'currentIndex = \K\d+' "$WALLPAPER_FILE")
+echo -e "Current index: ${YELLOW}$CURRENT_INDEX${NC}"
+
+# Count wallpapers (count occurrences of "name = " in the wallpapers list)
+WALLPAPER_COUNT=$(grep -c 'name = "' "$WALLPAPER_FILE")
+echo -e "Total wallpapers: ${YELLOW}$WALLPAPER_COUNT${NC}"
+
+# Calculate next index (wrap around)
+NEXT_INDEX=$(( (CURRENT_INDEX + 1) % WALLPAPER_COUNT ))
+echo -e "Next index: ${YELLOW}$NEXT_INDEX${NC}"
+
+# Update the currentIndex
+sed -i "s/currentIndex = $CURRENT_INDEX;/currentIndex = $NEXT_INDEX;/" "$WALLPAPER_FILE"
+
+echo -e "${GREEN}Successfully rotated wallpaper!${NC}"
+echo -e "  Old index: ${YELLOW}$CURRENT_INDEX${NC}"
+echo -e "  New index: ${YELLOW}$NEXT_INDEX${NC}"
+echo ""
+echo "Rebuild your system to apply the new wallpaper."