feat: model core, launcher, reproduction check and the first two skills

The core in modell/kjerne/ is an unmodified copy of sim.py, diagnose.py and
forlop.py from den-dynamiske-rettsstaten @2badc25, pinned by sha256.
kjor.py is the single entry point; kontroll.py reproduces the note's 22 data
files and printed results. Skills: diagnose and forlop (Norwegian).

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,55 @@
+# Not an installable distribution: no [project] table and no build backend.
+# Development environment (pip 25.1 or newer reads PEP 735 dependency groups):
+#   python3 -m venv .venv && .venv/bin/pip install --group dev
+# The plugin itself needs only the Python standard library; numpy and scipy are installed
+# at the user's request by `modell/kjor.py miljo --opprett` (pins in modell/requirements.txt).
+
+[dependency-groups]
+dev = [
+    "numpy==2.5.4",
+    "scipy==1.18.1",
+    "pytest==9.2.0",
+    "ruff==0.17.4",
+    "mypy==2.4.1",
+]
+
+[tool.ruff]
+target-version = "py39"           # kjor.py and kontroll.py must run on Python 3.9
+line-length = 120
+extend-exclude = ["modell/kjerne"]  # unmodified copy of the note's code: never linted or reformatted
+
+[tool.ruff.lint]
+select = ["ALL"]
+ignore = [
+    "T201",     # a command-line tool that talks to the user with print()
+    "S603",     # subprocess is always called with a fixed argument list, never through a shell
+    "INP001",   # modell/ and tests/ are folders of scripts, not packages
+    "N818",     # exception names are Norwegian (Bruksfeil already ends in "feil", error)
+    "D401",     # docstrings are Norwegian; the imperative-mood check only knows English verbs
+]
+
+[tool.ruff.lint.pydocstyle]
+convention = "pep257"
+
+[tool.ruff.lint.per-file-ignores]
+"tests/*" = [
+    "S101",     # pytest uses assert
+    "PLR2004",  # exit codes and counts are compared as literals in tests
+    "D103",     # test names describe the behaviour under test; a docstring would repeat them
+]
+
+[tool.mypy]
+strict = true
+files = ["modell", "tests"]
+mypy_path = "modell"
+exclude = ['^modell/kjerne/', '^\.venv/']
+# mypy 2.x cannot target Python 3.9 (it requires 3.10 or newer); Python 3.9 compatibility of
+# kjor.py and kontroll.py is checked by ruff (target-version) and by a test that runs them on 3.9.
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["modell"]
+addopts = "-m 'not treg'"
+markers = [
+    "treg: runs sim.py in full (about 1-2 minutes); deselected by default, run with -m treg",
+]