fix(update): route the self-update by install kind (apt/pip/source) — 0.37.1

rigdoctor update assumed a pip/venv install and ran 'python -m pip install', which
fails on a .deb (system python has no pip; you can't pip-upgrade a dpkg package).
Add updates.install_kind() (dpkg ownership / venv / source-checkout detection,
cached) and route apply_update: pip self-updates in place; apt and source installs
return guidance instead. CLI and the GUI Update button show the apt/git command.
Adds tests/test_updates.py.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_updates.py

@@ -0,0 +1,64 @@
+"""Tests for the M13 updater: install detection + routing the update to the right method."""
+
+import unittest
+from unittest import mock
+
+from rigdoctor.core import updates
+
+
+class InstallKindTests(unittest.TestCase):
+    def setUp(self):
+        updates.install_kind.cache_clear()
+
+    def tearDown(self):
+        updates.install_kind.cache_clear()
+
+    def test_apt_when_dpkg_owns_the_package(self):
+        with mock.patch.object(updates, "_dpkg_owns", return_value=True):
+            self.assertEqual(updates.install_kind(), "apt")
+
+    def test_pip_when_running_in_a_venv(self):
+        with mock.patch.object(updates, "_dpkg_owns", return_value=False), \
+             mock.patch.object(updates.sys, "prefix", "/opt/venv"), \
+             mock.patch.object(updates.sys, "base_prefix", "/usr"):
+            self.assertEqual(updates.install_kind(), "pip")
+
+
+class ApplyUpdateRoutingTests(unittest.TestCase):
+    def test_apt_returns_guidance_and_never_runs_pip(self):
+        with mock.patch.object(updates, "install_kind", return_value="apt"), \
+             mock.patch("subprocess.run") as run:
+            rc, out = updates.apply_update("v9.9.9")
+        self.assertEqual(rc, 1)
+        self.assertIn("apt install --only-upgrade", out)
+        run.assert_not_called()
+
+    def test_dev_returns_guidance_and_never_runs_pip(self):
+        with mock.patch.object(updates, "install_kind", return_value="dev"), \
+             mock.patch("subprocess.run") as run:
+            rc, out = updates.apply_update("v9.9.9")
+        self.assertIn("git pull", out)
+        run.assert_not_called()
+
+    def test_pip_install_runs_pip(self):
+        proc = mock.Mock(returncode=0, stdout="Successfully installed", stderr="")
+        with mock.patch.object(updates, "install_kind", return_value="pip"), \
+             mock.patch.object(updates, "load_token", return_value="TOK"), \
+             mock.patch("subprocess.run", return_value=proc) as run:
+            rc, _out = updates.apply_update("v1.2.3")
+        self.assertEqual(rc, 0)
+        cmd = run.call_args[0][0]
+        self.assertIn("pip", cmd)
+        self.assertIn("install", cmd)
+
+
+class UpdateHintTests(unittest.TestCase):
+    def test_apt_hint_names_the_apt_command(self):
+        self.assertIn("apt install --only-upgrade rigdoctor", updates.update_hint("apt"))
+
+    def test_dev_hint_says_git_pull(self):
+        self.assertIn("git pull", updates.update_hint("dev"))
+
+
+if __name__ == "__main__":
+    unittest.main()