Scaffold hello-world apps, test frameworks, and Gitea CI

- uv workspace tying nisse-core, nisse-dev, nisse-ops together
  (src layouts, workspace-sourced nisse-core dependency)
- Placeholder hello-world entry points for both agents, calling
  through nisse-core to exercise the package boundary
- pytest unit tests per package; integration tests (marker-gated)
  running the installed console scripts as subprocesses
- ruff lint + format, nisse_* declared first-party
- Gitea Actions workflow running lint, format check, unit and
  integration tests; scripts/check.sh mirrors it locally

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nisse-core/tests/test_greeting.py

@@ -0,0 +1,5 @@
+from nisse_core.greeting import greeting
+
+
+def test_greeting_includes_agent_name() -> None:
+    assert greeting("nisse-dev") == "Hello from nisse-dev, the house spirit is awake."