refactor: consolidate app configurations and utility scripts

- Move 32+ app-specific scripts from features/apps/scripts/ to features/scripts/utils/ for centralized packaging.
- Create individual Nix modules for orphaned app configurations (btop, kitty, tmux, etc.) in features/apps/ using xdg.configFile.
- Fix broken paths in core/system/makima.nix and features/apps/vscode.nix.
- Update VSCode configuration to use the modern 'profiles.default.userSettings' API, resolving deprecation warnings.
- Merge duplicate 'nomarchy-launch-walker' scripts into a single robust utility.
- Remove stale root 'config/' directory.
- Update README.md and docs/creating-themes.md to reflect the new architecture and keybindings.
- Ensure all modules are correctly imported and verified via nix flake check.

features/scripts/utils/nomarchy-launch-walker

@@ -3,10 +3,17 @@
 # Wrapper to launch walker with elephant provider, or fallback to rofi if walker is missing.
 
 if command -v walker >/dev/null 2>&1; then
+    # Ensure elephant is running before launching walker
     if ! pgrep -x elephant > /dev/null; then
         setsid uwsm-app -- elephant &
     fi
-    exec uwsm-app -- walker "$@"
+
+    # Ensure walker service is running
+    if ! pgrep -f "walker --gapplication-service" > /dev/null; then
+        setsid uwsm-app -- walker --gapplication-service &
+    fi
+
+    exec uwsm-app -- walker --width 644 --maxheight 300 --minheight 300 "$@"
 elif command -v rofi >/dev/null 2>&1; then
     # Convert walker arguments to rofi arguments if possible
     # This is a very basic mapping for --dmenu