renamed esp32c6 variants, so they are not included in release. added disclaimer about pioarduino builds

platformio.ini

@@ -67,6 +67,7 @@ lib_deps =
   file://arch/esp32/AsyncElegantOTA
 
 ; esp32c6 uses arduino framework 3.x
+; WARNING: experimental. pioarduino on esp32c6 needs work - it's not considered stable and has issues.
 [esp32c6_base]
 extends = esp32_base
 platform = https://github.com/pioarduino/platform-espressif32/releases/download/53.03.12/platform-espressif32.zip