refactor: convert script to automtu package with CI workflow

https://chatgpt.com/share/697112b2-0410-800f-93ff-9372b603d43f

tests/unit/test_net.py

@@ -0,0 +1,49 @@
+import unittest
+from unittest.mock import patch
+
+import automtu.net as net
+
+
+class TestNet(unittest.TestCase):
+    def test_detect_egress_iface_parses_default_route_and_ignores_vpn(self) -> None:
+        # Simulate: ip route show default -> dev wg0 first, then eth0
+        ip4_default = (
+            "default via 10.0.0.1 dev wg0 proto dhcp src 10.0.0.2 metric 100\n"
+        )
+        ip6_default = "default via fe80::1 dev eth0 proto ra metric 100\n"
+
+        def fake_run(cmd: list[str]) -> str:
+            if cmd[:4] == ["ip", "-4", "route", "show"]:
+                return ip4_default.strip()
+            if cmd[:4] == ["ip", "-6", "route", "show"]:
+                return ip6_default.strip()
+            return ""
+
+        with (
+            patch("automtu.net._run", side_effect=fake_run),
+            patch("automtu.net.iface_exists", return_value=True),
+        ):
+            # ignore_vpn=True -> should skip wg0 and pick eth0
+            self.assertEqual(net.detect_egress_iface(ignore_vpn=True), "eth0")
+
+            # ignore_vpn=False -> first seen is wg0
+            self.assertEqual(net.detect_egress_iface(ignore_vpn=False), "wg0")
+
+    def test_default_route_uses_iface_true_false(self) -> None:
+        ip4_default = "default via 10.0.0.1 dev eth0\n"
+        ip6_default = ""
+
+        def fake_run(cmd: list[str]) -> str:
+            if cmd[:4] == ["ip", "-4", "route", "show"]:
+                return ip4_default.strip()
+            if cmd[:4] == ["ip", "-6", "route", "show"]:
+                return ip6_default.strip()
+            return ""
+
+        with patch("automtu.net._run", side_effect=fake_run):
+            self.assertTrue(net.default_route_uses_iface("eth0"))
+            self.assertFalse(net.default_route_uses_iface("wg0"))
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)