fix(ble,usb): three bugs from BLE audit

1. USB takeover opcode mismatch
   ZephyrCompanionUSB.cpp checked payload[0] == 0x03 with a comment
   claiming CMD_APP_START, but CMD_APP_START is 0x01 (0x03 is
   CMD_SEND_CHANNEL_TXT_MSG). The USB handshake silently dropped the
   companion app's first frame on every connection; the app appeared
   broken over USB until the user happened to send a channel message.

2. CMD_SET_ADVERT_NAME didn't propagate to BLE adv data
   Name changes were persisted to prefs but the advertising payload
   and GATT device name kept the old value until reboot. Added
   zephcore_ble_update_name() and called it from the handler.

3. No advertising-health watchdog
   If bt_le_adv_start() ever failed transiently (HCI timeout,
   controller pacing), the device would silently stop advertising
   and stay undiscoverable until reboot. Added an adv_running flag
   and a 5s watchdog in the companion housekeeping handler that
   nudges adv back on if it stops outside a connection. Tracks
   Arduino nrf52's equivalent 10s watchdog.

zephcore/app/CompanionMesh.cpp

@@ -1899,6 +1899,8 @@ bool CompanionMesh::handleProtocolFrame(const uint8_t *data, size_t len)
 			memcpy(prefs.node_name, &data[1], nlen);
 			prefs.node_name[nlen] = '\0';
 			_store->savePrefs(prefs);
+			/* Push the new name to BLE so scanners see it without a reboot. */
+			zephcore_ble_update_name(prefs.node_name);
 		}
 		sendPacketOk();
 		return true;