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>

scripts/check.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+# Run everything CI runs: lint, format check, unit tests, integration tests.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+uv sync --all-packages
+uv run ruff check .
+uv run ruff format --check .
+uv run pytest -m "not integration"
+uv run pytest -m integration