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-dev/src/nisse_dev/main.py

@@ -0,0 +1,11 @@
+"""Placeholder entry point for the dev agent."""
+
+from nisse_core.greeting import greeting
+
+
+def main() -> None:
+    print(greeting("nisse-dev"))
+
+
+if __name__ == "__main__":
+    main()