Stop the C6 reflash loop: accept factory 2.12.11 slave (gate >=2)

The BT-off custom slave (2.12.12) can't survive the C6's OTA rollback
protection: it flashes, the C6 boots it, reverts to 2.12.11, host
reflashes -> ~30s reboot loop, worse than the wedge. BLE-coex
hypothesis is UNTESTABLE via OTA (custom slaves won't stick; needs
direct C6 UART flash, out of scope tonight). Reverted to the
self-healing 2.12.11 baseline: ~5-13min MTBF, 15s auto-recovery.
That is the shippable overnight state.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

firmware/main/c6_ota.c

@@ -44,8 +44,8 @@ static void c6_ota_task(void *arg)
     vTaskDelay(pdMS_TO_TICKS(8000)); /* let the hosted transport settle */
     esp_hosted_coprocessor_fwver_t v = { 0 };
     if (esp_hosted_get_coprocessor_fwversion(&v) == ESP_OK &&
-        v.major1 == 2 && v.minor1 == 12 && v.patch1 == 12) {
-        ESP_LOGI(TAG, "C6 fw already 2.12.12-btfree — no OTA needed");
+        v.major1 >= 2) {  /* 2.12.11 factory image is good enough; custom slaves roll back */
+        ESP_LOGI(TAG, "C6 fw already 2.x — no OTA needed");
         vTaskDelete(NULL);
         return;
     }