feat(cmdline): use C&C topic with response polling

- Rewrite cmdline to send commands via ntfy and wait for response
- Add NtfyResponsePoller class for serial-port-like interface
- Add integration tests for ntfy topics (test read/write)
- Add NTFY_CC_TOPIC export to config

tests/test_ntfy_integration.py

@@ -0,0 +1,101 @@
+"""
+Integration tests for ntfy topics.
+"""
+
+import json
+import time
+import urllib.request
+
+
+class TestNtfyTopics:
+    def test_cc_topic_exists_and_writable(self):
+        """Verify C&C topic exists and accepts messages."""
+        from engine.config import NTFY_CC_TOPIC
+
+        topic_url = NTFY_CC_TOPIC.replace("/json", "")
+        test_message = f"test_{int(time.time())}"
+
+        req = urllib.request.Request(
+            topic_url,
+            data=test_message.encode("utf-8"),
+            headers={
+                "User-Agent": "mainline-test/0.1",
+                "Content-Type": "text/plain",
+            },
+            method="POST",
+        )
+
+        try:
+            with urllib.request.urlopen(req, timeout=10) as resp:
+                assert resp.status == 200
+        except Exception as e:
+            raise AssertionError(f"Failed to write to C&C topic: {e}") from e
+
+    def test_message_topic_exists_and_writable(self):
+        """Verify message topic exists and accepts messages."""
+        from engine.config import NTFY_TOPIC
+
+        topic_url = NTFY_TOPIC.replace("/json", "")
+        test_message = f"test_{int(time.time())}"
+
+        req = urllib.request.Request(
+            topic_url,
+            data=test_message.encode("utf-8"),
+            headers={
+                "User-Agent": "mainline-test/0.1",
+                "Content-Type": "text/plain",
+            },
+            method="POST",
+        )
+
+        try:
+            with urllib.request.urlopen(req, timeout=10) as resp:
+                assert resp.status == 200
+        except Exception as e:
+            raise AssertionError(f"Failed to write to message topic: {e}") from e
+
+    def test_cc_topic_readable(self):
+        """Verify we can read messages from C&C topic."""
+        from engine.config import NTFY_CC_TOPIC
+
+        test_message = f"integration_test_{int(time.time())}"
+        topic_url = NTFY_CC_TOPIC.replace("/json", "")
+
+        req = urllib.request.Request(
+            topic_url,
+            data=test_message.encode("utf-8"),
+            headers={
+                "User-Agent": "mainline-test/0.1",
+                "Content-Type": "text/plain",
+            },
+            method="POST",
+        )
+
+        try:
+            urllib.request.urlopen(req, timeout=10)
+        except Exception as e:
+            raise AssertionError(f"Failed to write to C&C topic: {e}") from e
+
+        time.sleep(1)
+
+        poll_url = f"{NTFY_CC_TOPIC}?poll=1&limit=1"
+        req = urllib.request.Request(
+            poll_url,
+            headers={"User-Agent": "mainline-test/0.1"},
+        )
+
+        try:
+            with urllib.request.urlopen(req, timeout=10) as resp:
+                body = resp.read().decode("utf-8")
+                if body.strip():
+                    data = json.loads(body.split("\n")[0])
+                    assert isinstance(data, dict)
+        except Exception as e:
+            raise AssertionError(f"Failed to read from C&C topic: {e}") from e
+
+    def test_topics_are_different(self):
+        """Verify C&C and message topics are different."""
+        from engine.config import NTFY_CC_TOPIC, NTFY_TOPIC
+
+        assert NTFY_CC_TOPIC != NTFY_TOPIC
+        assert "_cc" in NTFY_CC_TOPIC