Add debug flag and config init support

Introduce a `--debug` option and an `Init` subcommand to the CLI.
Add a new `config` module with loader and schema types for reading and
creating a default `veil.yaml` (supporting a local debug config path).
Update `.gitignore`, `default.nix`, and `flake.nix` comments to
reference
the templates directory.
Provide an example configuration template and integrate it into the
application’s entry point.

default.nix

@@ -33,7 +33,7 @@ in
     passthru.updateScript = nix-update-script {};
 
     # postInstall = ''
-    #   cp static files
+    #   cp -r templates $out/bin
     # '';
 
     meta = {