feat(ntfy): separate C&C topic from message ingestion

- Add ntfy_cc_topic config for command and control
- Add separate NtfyPoller for C&C in StreamController
- Implement serial-port-like interface: commands are executed and responses are sent back to the same topic
- Update cmdline.py to use C&C topic

engine/controller.py

@@ -3,6 +3,7 @@ Stream controller - manages input sources and orchestrates the render stream.
 """
 
 from engine.config import Config, get_config
+from engine.effects.controller import handle_effects_command
 from engine.eventbus import EventBus
 from engine.events import EventType, StreamEvent
 from engine.mic import MicMonitor
@@ -18,6 +19,7 @@ class StreamController:
         self.event_bus = event_bus
         self.mic: MicMonitor | None = None
         self.ntfy: NtfyPoller | None = None
+        self.ntfy_cc: NtfyPoller | None = None
 
     def initialize_sources(self) -> tuple[bool, bool]:
         """Initialize microphone and ntfy sources.
@@ -35,7 +37,38 @@ class StreamController:
         )
         ntfy_ok = self.ntfy.start()
 
-        return bool(mic_ok), ntfy_ok
+        self.ntfy_cc = NtfyPoller(
+            self.config.ntfy_cc_topic,
+            reconnect_delay=self.config.ntfy_reconnect_delay,
+            display_secs=5,
+        )
+        self.ntfy_cc.subscribe(self._handle_cc_message)
+        ntfy_cc_ok = self.ntfy_cc.start()
+
+        return bool(mic_ok), ntfy_ok and ntfy_cc_ok
+
+    def _handle_cc_message(self, event) -> None:
+        """Handle incoming C&C message - like a serial port control interface."""
+        import urllib.request
+
+        cmd = event.body.strip() if hasattr(event, "body") else str(event).strip()
+        if not cmd.startswith("/"):
+            return
+
+        response = handle_effects_command(cmd)
+
+        topic_url = self.config.ntfy_cc_topic.replace("/json", "")
+        data = response.encode("utf-8")
+        req = urllib.request.Request(
+            topic_url,
+            data=data,
+            headers={"User-Agent": "mainline/0.1", "Content-Type": "text/plain"},
+            method="POST",
+        )
+        try:
+            urllib.request.urlopen(req, timeout=5)
+        except Exception:
+            pass
 
     def run(self, items: list) -> None:
         """Run the stream with initialized sources."""