[ota] Fix clang-tidy goto-jumps-init and set error_code on timeout

Address two issues on the new data-loop timeout:

- clang-tidy ESP32 Arduino flagged "cannot jump from this goto statement to its label" at the existing pre-loop `goto error` sites because the new `uint32_t last_data_ms = millis();` declaration sat between them and the `error:` label, so the jumps would skip past its initialization. Move the declaration up next to the other handle_data_ locals (`total`, `last_progress`) and just assign it before the loop entry. The earlier gotos no longer cross an init.

- Copilot pointed out the new timeout `goto error` left `error_code` at `OTA_RESPONSE_OK` (set by `backend_->begin()`), so the device would write OK back to the uploader even though it was aborting. Set `error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN` before the goto so the uploader receives a correct failure code.

esphome/components/esphome/ota/ota_esphome.cpp

@@ -292,6 +292,7 @@ void ESPHomeOTAComponent::handle_data_() {
   bool update_started = false;
   size_t total = 0;
   uint32_t last_progress = 0;
+  uint32_t last_data_ms = 0;
   uint8_t buf[OTA_BUFFER_SIZE];
   char *sbuf = reinterpret_cast<char *>(buf);
   size_t ota_size;
@@ -355,10 +356,11 @@ void ESPHomeOTAComponent::handle_data_() {
   // can't wedge the device indefinitely. Without this, the loop only exits
   // on actual data, EOF, or a non-EWOULDBLOCK error from read(), and lwIP
   // TCP keepalive isn't enabled here.
-  uint32_t last_data_ms = millis();
+  last_data_ms = millis();
   while (total < ota_size) {
     if (millis() - last_data_ms > OTA_SOCKET_TIMEOUT_DATA) {
       ESP_LOGW(TAG, "No data received for %u ms", (unsigned) OTA_SOCKET_TIMEOUT_DATA);
+      error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
       goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
     }
     size_t remaining = ota_size - total;