feat: add Docker MTU apply support and docker-ordered persistence

https://chatgpt.com/share/69733e45-96ec-800f-9aad-0cac7306dedd

tests/unit/test_docker.py

@@ -0,0 +1,49 @@
+import unittest
+from unittest.mock import patch
+
+import automtu.docker as docker
+
+
+class TestDocker(unittest.TestCase):
+    def test_detect_docker_ifaces_explicit_dedup_and_drop_unknown(self) -> None:
+        # explicit args are repeatable and/or comma-separated
+        args = ["docker0,br-abc,unknown0", "br-abc,docker0"]
+
+        def fake_iface_exists(name: str) -> bool:
+            return name in {"docker0", "br-abc"}  # unknown0 does not exist
+
+        with patch("automtu.docker.iface_exists", side_effect=fake_iface_exists):
+            got = docker.detect_docker_ifaces(args, include_user_bridges=True)
+
+        # preserve order, de-dup, drop unknown
+        self.assertEqual(got, ["docker0", "br-abc"])
+
+    def test_detect_docker_ifaces_auto_detect_docker0_only(self) -> None:
+        # no explicit args -> auto detect
+        def fake_iface_exists(name: str) -> bool:
+            return name == "docker0"
+
+        with patch("automtu.docker.iface_exists", side_effect=fake_iface_exists):
+            got = docker.detect_docker_ifaces(None, include_user_bridges=False)
+
+        self.assertEqual(got, ["docker0"])
+
+    def test_detect_docker_ifaces_auto_detect_includes_user_bridges(self) -> None:
+        # docker0 exists + br-* exists in list_ifaces -> included if include_user_bridges=True
+        def fake_iface_exists(name: str) -> bool:
+            return name in {"docker0", "br-abc"}  # br-abc exists, br-nope does not
+
+        with (
+            patch("automtu.docker.iface_exists", side_effect=fake_iface_exists),
+            patch(
+                "automtu.docker.list_ifaces",
+                return_value=["lo", "eth0", "br-abc", "br-nope", "wg0"],
+            ),
+        ):
+            got = docker.detect_docker_ifaces(None, include_user_bridges=True)
+
+        self.assertEqual(got, ["docker0", "br-abc"])
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)