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.

.gitignore

@@ -1,4 +1,5 @@
 /target
 /result
+/local-config
 
 veil-rs.log