docs: describe the TCP transport, multiplexing and TCPStreamJoin in README, architecture and StreamHub docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Docs/StreamHub-API.md

@@ -33,6 +33,9 @@ Reply (unicast): `{"type":"pong"}`.
 - `addr` — `host:port` of the UDPStreamer control port.
 - `multicastGroup` / `dataPort` — optional; if present the hub joins the
   multicast group for DATA and keeps a TCP control connection for CONNECT/CONFIG.
+- `transport` (`"udp"` default, or `"tcp"`) and `streamName` — for a TCP source, the
+  `TCPStreamService` stream to subscribe to. A comma list (`"a,b"`) multiplexes several
+  streams over one connection and adds one source per stream, labelled `<label>_<stream>`.
 - The hub assigns ids `s1`, `s2`, … and broadcasts an updated `sources` event.
 
 ### `removeSource`
@@ -421,6 +424,7 @@ warning.
 [
   {"label": "wave", "addr": "127.0.0.1:44500"},
   {"label": "mc",   "addr": "127.0.0.1:44501", "multicastGroup": "239.0.0.1", "dataPort": 44502},
+  {"label": "svc",  "addr": "127.0.0.1:44500", "transport": "tcp", "streamName": "fast,slow"},
   {"source": "wave", "signal": "Adc", "scale": 0.00030518, "offset": -1.25, "unit": "V"}
 ]
 ```