Add goTool web dashboard with UART auto-reconnect.

Serve polls the master over UART and pushes live state via WebSocket;
reopens the serial port when the device is unplugged and comes back.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/README.md

@@ -26,6 +26,7 @@ go run . -port /dev/ttyUSB0 clients
 | `clients` | `0x04` | Lists slaves registered on the master via ESP-NOW |
 | `unicast-test` | `0x07` | Sends ESP-NOW unicast test to one slave (`-client`, `-seq`) |
 | `test` | — | Run an automated scenario (JSON configs under `testdata/`) |
+| `serve` | — | Web dashboard at `http://localhost:8080` (WebSocket live updates) |
 
 `clients` requires slaves to have responded to master discover broadcasts first.
 
@@ -43,6 +44,20 @@ With a complete bench config, `-port` is optional for `test` (uses `uart.master`
 
 See [`testdata/README.md`](testdata/README.md) for the JSON schema.
 
+### Web dashboard
+
+Polls the master over UART and pushes state to the browser via WebSocket (Alpine.js + Bootstrap 5).
+
+```bash
+go run . -port /dev/ttyUSB0 serve
+go run . -port /dev/ttyUSB0 serve -addr :8080 -interval 2s
+make gotool-serve PORT=/dev/ttyUSB0
+```
+
+Open [http://localhost:8080](http://localhost:8080) — shows master firmware info and the ESP-NOW client table from `CLIENT_INFO`.
+
+If the UART device is unplugged or the port disappears, `serve` keeps running and retries on each poll interval; the UI shows **UART off** until the port is available again.
+
 ```bash
 go run . -port /dev/ttyUSB0 unicast-test -client 16 -seq 42
 ```