Implement cli init command

closes #1

tests/e2e/test_init.py

@@ -0,0 +1,36 @@
+import subprocess
+import yaml
+
+
+def test_init_creates_site(tmp_path):
+    site_dir = tmp_path / "newsite"
+    result = subprocess.run(
+        ["ossg", "--site", str(site_dir), "init"],
+        input="My Site\nhttps://example.com\n\n\n",
+        capture_output=True,
+        text=True,
+    )
+    assert result.returncode == 0, result.stderr
+
+    config = yaml.safe_load((site_dir / "config.yml").read_text())
+    assert config == {
+        "name": "My Site",
+        "base_url": "https://example.com/",
+        "template": "plain",
+        "items_per_page": 20,
+    }
+    assert (site_dir / "content").is_dir()
+
+
+def test_init_refuses_non_empty_dir(tmp_path):
+    (tmp_path / "some_file").touch()
+
+    result = subprocess.run(
+        ["ossg", "--site", str(tmp_path), "init"],
+        input="My Site\n\n\n\n",
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.returncode == 1
+    assert "is not empty" in result.stdout