Add UART SET_LOG_LEVEL for runtime master ESP-IDF logging.

Expose the command via goTool CLI/REST and dashboard controls so log verbosity can be tuned without reflashing.

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

goTool/docs/API_REST.md

@@ -282,6 +282,39 @@ Content-Type: application/json
 {"client_id": 16}
 ```
 
+### Log level (master ESP-IDF console)
+
+Runtime get/set of the **global** log filter on the master (`esp_log_level_set("*", …)`). Output goes to **UART0** (USB debug, 115200), not the host protocol UART (GPIO 2/3, 921600).
+
+```http
+GET /api/log-level
+POST /api/log-level
+Content-Type: application/json
+{"write": true, "level": 3}
+```
+
+| `level` | Meaning |
+|---------|---------|
+| 0 | None (no log output) |
+| 1 | Error |
+| 2 | Warn |
+| 3 | Info |
+| 4 | Debug |
+| 5 | Verbose |
+
+```json
+{"success": true, "level": 3}
+```
+
+**CLI:**
+
+```bash
+go run . -port /dev/ttyUSB0 log-level
+go run . -port /dev/ttyUSB0 log-level -set -level 3
+```
+
+Dashboard: Master card → dropdown **ESP Log-Level** with **Lesen** / **Setzen**.
+
 ### OTA (master UART upload)
 
 ```http
@@ -329,5 +362,6 @@ Same as external API:
 | Alle Slaves deadzone | `all_clients` + `slaves_only` on POST |
 | Unicast test | `POST /api/unicast-test` |
 | Echo ping | `POST /api/echo-ping` (per-slave latency; UI shows Host ms + ESP ms) |
+| Master log level | `GET` / `POST /api/log-level` or CLI `log-level` |
 | Tap notify S/D/T | `PUT /api/clients/{id}/tap-notify` |
 | Tap receive (UI) | Live stream + tap notify; see WebSocket doc for external API |