add ESP32 build system with xtensa-esp-elf toolchain

src/spider/main_esp32.cpp

@@ -1,8 +0,0 @@
-// ESP32 entry point for Spider Runtime
-// This replaces SpiderRuntime.cpp for microcontroller builds
-#include "SpiderRuntime.hpp"
-
-int main() {
-    // TODO: initialize Spider runtime for ESP32
-    return 0;
-}