feat(streaming): introduce WebSocket Streaming API bridging event bus

ApiServer: add AsyncWebSocket at /ws; accept JSON {event, payload} (string or object) and dispatch via ctx.fire; mirror all local events to clients using NodeContext::onAny.\nNodeContext: add onAny subscriber API.\nNeoPatternService: add api/neopattern/color event to set solid color.\nCluster: centralize cluster/broadcast sending in core; services delegate.\nAPI: add generic /api/node/event and /api/cluster/event endpoints in respective services.\nTests: add ws-color-client, ws-cluster-broadcast-color, http-cluster-broadcast-color.\nDocs: add StreamingAPI.md; update README and test/README.\nFixes: robust WS JSON parsing on ESP8266 and payload handling.

docs/StreamingAPI.md

@@ -0,0 +1,71 @@
+## Streaming API (WebSocket)
+
+### Overview
+
+The streaming API exposes an event-driven WebSocket at `/ws`. It bridges between external clients and the internal event bus:
+
+- Incoming WebSocket JSON `{ event, payload }` → `ctx.fire(event, payload)`
+- Local events → broadcasted to all connected WebSocket clients as `{ event, payload }`
+
+This allows real-time control and observation of the system without polling.
+
+### URL
+
+- `ws://<device-ip>/ws`
+
+### Message Format
+
+- Client → Device
+```json
+{
+  "event": "<event-name>",
+  "payload": "<json-string>" | { /* inline JSON */ }
+}
+```
+
+- Device → Client
+```json
+{
+  "event": "<event-name>",
+  "payload": "<json-string>"
+}
+```
+
+Notes:
+- The device accepts `payload` as a string or a JSON object/array. Objects are serialized into a string before dispatching to local subscribers to keep a consistent downstream contract.
+- A minimal ack `{ "ok": true }` is sent after a valid inbound message.
+
+### Event Bus Integration
+
+- The WebSocket registers an `onAny` subscriber to `NodeContext` so that all local events are mirrored to clients.
+- Services should subscribe to specific events via `ctx.on("<name>", ...)`.
+
+### Examples
+
+1) Set a solid color on NeoPattern:
+```json
+{
+  "event": "api/neopattern/color",
+  "payload": { "color": "#FF0000", "brightness": 128 }
+}
+```
+
+2) Broadcast a cluster event (delegated to core):
+```json
+{
+  "event": "cluster/broadcast",
+  "payload": {
+    "event": "api/neopattern/color",
+    "data": { "color": "#00FF00", "brightness": 128 }
+  }
+}
+```
+
+### Reference Implementation
+
+- WebSocket setup and bridging are implemented in `ApiServer`.
+- Global event subscription uses `NodeContext::onAny`.
+
+Related docs:
+- [`ClusterBroadcast.md`](./ClusterBroadcast.md) — centralized UDP broadcasting and CLUSTER_EVENT format
+