feat: add the aegis-gitea-mcp setup command

Verifies the Gitea instance, token and scopes, registers or reuses the aegis-gitea-mcp OAuth app, generates missing secrets and writes a 0600 env file from the template. Prints client configs and deployment snippets without any secret value.

tests/test_cli.py

@@ -15,7 +15,7 @@ def test_version_prints_package_version(capsys: pytest.CaptureFixture[str]) -> N
     assert capsys.readouterr().out.strip() == __version__
 
 
-@pytest.mark.parametrize("argv", [[], ["serve"], ["serve", "--transport", "http"], ["setup"]])
+@pytest.mark.parametrize("argv", [[], ["serve"], ["serve", "--transport", "http"]])
 def test_unbuilt_commands_exit_2(argv: list[str], capsys: pytest.CaptureFixture[str]) -> None:
     assert main(argv) == 2
     captured = capsys.readouterr()