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/upgrade.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+BLUE='\033[0;34m'
+NC='\033[0m' # No Color
+
+REPO_ROOT="${REPO_ROOT:-$(git rev-parse --show-toplevel 2>/dev/null || pwd)}"
+
+echo -e "${BLUE}========================================${NC}"
+echo -e "${BLUE}  NixOS Configuration Major Upgrade${NC}"
+echo -e "${BLUE}========================================${NC}"
+echo ""
+
+# Step 1: Update flake inputs
+echo -e "${GREEN}[1/4] Updating flake inputs...${NC}"
+cd "$REPO_ROOT"
+nix flake update
+echo ""
+
+# Step 2: Update Doom Emacs
+echo -e "${GREEN}[2/4] Updating Doom Emacs...${NC}"
+"$REPO_ROOT/scripts/update-doomemacs.sh"
+echo ""
+
+# Step 3: Update Claude Code
+echo -e "${GREEN}[3/4] Updating Claude Code...${NC}"
+"$REPO_ROOT/packages/claude-code/update.sh"
+echo ""
+
+# Step 4: Rotate wallpaper
+echo -e "${GREEN}[4/4] Rotating wallpaper...${NC}"
+"$REPO_ROOT/scripts/rotate-wallpaper.sh"
+echo ""
+
+echo -e "${BLUE}========================================${NC}"
+echo -e "${GREEN}Upgrade complete!${NC}"
+echo -e "${BLUE}========================================${NC}"
+echo ""
+echo "Next steps:"
+echo "  1. Review changes: git diff"
+echo "  2. Rebuild system: sudo nixos-rebuild switch --flake ."
+echo "  3. If satisfied, commit: git add -A && git commit -m 'chore: Major upgrade'"