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.

flake.nix

@@ -234,15 +234,44 @@
     apps = nixpkgs.lib.genAttrs [ "x86_64-linux" "aarch64-linux" "aarch64-darwin" ] (system:
       let
         pkgs = import nixpkgs { inherit system; };
+        commonDeps = [ pkgs.curl pkgs.jq pkgs.nix pkgs.git pkgs.gnused pkgs.gnugrep pkgs.coreutils pkgs.gawk ];
+
         update-doomemacs = pkgs.writeShellScriptBin "update-doomemacs" ''
-          export PATH="${pkgs.lib.makeBinPath [ pkgs.curl pkgs.jq pkgs.nix pkgs.git pkgs.gnused pkgs.gnugrep pkgs.coreutils ]}:$PATH"
+          export PATH="${pkgs.lib.makeBinPath commonDeps}:$PATH"
           ${builtins.readFile ./scripts/update-doomemacs.sh}
         '';
+
+        update-claude-code = pkgs.writeShellScriptBin "update-claude-code" ''
+          export PATH="${pkgs.lib.makeBinPath commonDeps}:$PATH"
+          ${builtins.readFile ./packages/claude-code/update.sh}
+        '';
+
+        rotate-wallpaper = pkgs.writeShellScriptBin "rotate-wallpaper" ''
+          export PATH="${pkgs.lib.makeBinPath commonDeps}:$PATH"
+          ${builtins.readFile ./scripts/rotate-wallpaper.sh}
+        '';
+
+        upgrade = pkgs.writeShellScriptBin "upgrade" ''
+          export PATH="${pkgs.lib.makeBinPath commonDeps}:$PATH"
+          ${builtins.readFile ./scripts/upgrade.sh}
+        '';
       in {
         update-doomemacs = {
           type = "app";
           program = "${update-doomemacs}/bin/update-doomemacs";
         };
+        update-claude-code = {
+          type = "app";
+          program = "${update-claude-code}/bin/update-claude-code";
+        };
+        rotate-wallpaper = {
+          type = "app";
+          program = "${rotate-wallpaper}/bin/rotate-wallpaper";
+        };
+        upgrade = {
+          type = "app";
+          program = "${upgrade}/bin/upgrade";
+        };
       }
     );
   };