Fix Linux Emscripten build: replace gethostbyname + add build_web.sh

[Copilot]

Two linker errors blocked the web-build from compiling on Linux with modern emsdk. Fixes both without touching non-web platform code.

Root causes

• gethostbyname undefined: Emscripten removed this symbol; two call sites existed inside RAKNET_SUPPORT_IPV6==0 branches of SocketLayer.cpp.
• emscripten_websocket_send_binary undefined: Caused by adding -sPROXY_POSIX_SOCKETS=1 without linking libwebsockets. Avoided entirely by choosing Option 2 (singleplayer-only for web).

Changes

web-build/src/raknet/SocketLayer.cpp

Replace both gethostbyname usages with getaddrinfo under #ifdef __EMSCRIPTEN__. Non-web builds unaffected.

// DomainNameToIP_Old() and GetMyIP_Win32() — same pattern:
#ifdef __EMSCRIPTEN__
    struct addrinfo hints, *res;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family   = AF_INET;
    hints.ai_socktype = SOCK_DGRAM;
    if (getaddrinfo(domainName, NULL, &hints, &res) != 0 || res == NULL)
        return 0;
    // ... extract addr, freeaddrinfo, return
#else
    struct hostent *phe = gethostbyname(domainName);  // original path
    // ...
#endif

web-build/project/emscripten/build_web.sh (new)

Linux bash equivalent of build_web.ps1:

• LF line endings, executable
• --clean: wipes obj/ and out/ before rebuild
• --serve: runs a Python 3 server with COOP/COEP headers required for SharedArrayBuffer
• Output to web-build/out/index.{html,js,wasm}
• No -sPROXY_POSIX_SOCKETS — RakNet UDP multiplayer is not viable in browsers; singleplayer links cleanly

./web-build/project/emscripten/build_web.sh --clean   # full rebuild
./web-build/project/emscripten/build_web.sh --serve   # build + serve localhost:8000

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