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-webapp-handler-hey

@@ -0,0 +1,11 @@
+#!/bin/bash
+url="$1"
+web_url="https://app.hey.com"
+
+# Handle mailto: URLs
+if [[ $url =~ ^mailto: ]]; then
+  email=$(echo "$url" | sed 's/mailto://')
+  web_url="https://app.hey.com/messages/new?to=$email"
+fi
+
+exec nomarchy-launch-webapp "$web_url"