Add in-app speaker discovery and connection guide

docs/ARCHITECTURE.md

@@ -14,6 +14,7 @@ the package or running `--help` does not load Tk or Bleak.
 | `ble_link.py` | Bleak connection, notifications, characteristic writes |
 | `link.py`, `transport.py` | Experimental RFCOMM and serial adapters |
 | `gui.py` | Tk controls and event rendering |
+| `discovery.py` | Read-only BLE discovery, unnamed model matching, and selectable labels |
 | `cli.py`, `__main__.py` | Installed command and backwards-compatible module entry |
 | `ble_probe.py`, `probe.py` | Endpoint diagnostics |
 | `windows_bluetooth.py` | Experimental RFCOMM initialization |
@@ -41,6 +42,11 @@ async event loop lives entirely within the worker thread. The GUI submits
 payloads through a bounded command queue and consumes events through another
 queue; workers never call Tk methods.
 
+Discovery uses a separate bounded-duration worker and the same event queue.
+It returns plain speaker records without opening a GATT connection. Tk maps a
+selected label to its address; manual addresses remain supported. Scanning is
+disabled while a connection is active so scans do not compete with BLE traffic.
+
 BLE notifications enter a bounded async queue and can contain partial or
 combined packets. The decoder retains framing state between notifications.
 Queue overflow terminates the connection rather than silently losing framing.