controller: Phase 3 — Python sidecar skeleton (MQTT + ZMQ + HTTP + HA Discovery)

cuda-grid-controller (Python 3.11+) — control plane между HA/MQTT/HTTP
и FFmpeg's vf_cuda_grid filter через ZMQ.

Modules (~700 LOC Python):
- config.py — Pydantic schema (broker, instances[], ha_discovery, http, log) + YAML loader
- layouts.py — registry известных layouts (sync с vf_cuda_grid.c Phase 2)
- ha_discovery.py — HA MQTT Discovery payloads (select.layout, sensor.current_layout,
  binary_sensor.online per instance + global device entry)
- zmq_client.py — async ZMQ REQ socket к FFmpeg zmq filter
  (target command args → reply parsing)
- state.py — in-memory ControllerState (active_layout per instance, asyncio.Lock)
- mqtt_loop.py — aiomqtt async loop: subscribe cuda_grid/cmd/<inst>/+/+,
  publish cuda_grid/state/* (retained) + cuda_grid/event/*, LWT, HA status reconnect
- dispatch.py — CommandDispatcher: layout.set action → ZMQ send_command + state update + events
- http_api.py — FastAPI: /health, /layouts, /state, POST /layout/{inst}/set
- __main__.py — typer CLI, asyncio.gather(mqtt_loop, uvicorn.server)

Examples + Dockerfile:
- examples/controller.yaml — 2 instances (livingroom_tv, public_stream)
- Dockerfile — python:3.11-slim, ENTRYPOINT cuda-grid-controller
- README — overview, usage, FFmpeg side filter graph

End-to-end flow ready:
  HA dashboard → MQTT → controller → ZMQ → FFmpeg process_command → layout switch
  ↓
  state публикуется обратно в MQTT → HA UI обновляется

Phase 3 deliverable per gx/vf-cuda-grid#1. Phase 4 = overlays (rect/text/icon).

controller/cuda_grid_controller/state.py

@@ -0,0 +1,33 @@
+"""In-memory state controller'а."""
+
+from __future__ import annotations
+
+import asyncio
+from dataclasses import dataclass, field
+
+
+@dataclass
+class InstanceState:
+    name: str
+    active_layout: str
+    # Future: fps_out, dropped_frames, motion_cameras, last_event_ts
+
+
+@dataclass
+class ControllerState:
+    instances: dict[str, InstanceState] = field(default_factory=dict)
+    _lock: asyncio.Lock = field(default_factory=asyncio.Lock)
+
+    async def set_layout(self, instance: str, layout: str) -> None:
+        async with self._lock:
+            st = self.instances.get(instance)
+            if st is None:
+                st = InstanceState(name=instance, active_layout=layout)
+                self.instances[instance] = st
+            else:
+                st.active_layout = layout
+
+    async def get_layout(self, instance: str) -> str | None:
+        async with self._lock:
+            st = self.instances.get(instance)
+            return st.active_layout if st else None