archlens init should generate a usable config

[mircealungu]

Problem

Running `archlens init` from a project directory generates a config with empty `rootFolder` and `name`, which immediately fails schema validation when you run `archlens render`.

Current template:
```json
{
"name": "",
"rootFolder": "",
"fileExtensions": [".cs"]
}
```

The `name` field is populated with `os.path.basename(os.getcwd())`, but `rootFolder` is left empty, violating the schema's `minLength: 1` constraint.

Expected behavior

`archlens init` followed by `archlens render` should just work with sensible defaults:

• `rootFolder` should default to `"."` (current directory)
• `fileExtensions` should be auto-detected by scanning for source files in the directory
• Or at minimum, the template should have `rootFolder: "."` so it passes validation

Steps to reproduce

```bash
cd some-csharp-project
archlens init
archlens render # fails with ValidationError: '' should be non-empty
```