Replace direct cargo xwin execution with PATH traversal to locate actual cargo-xwin binary outside script's own directory. Add error handling with installation instructions when binary not found. Skip script's own directory and empty PATH entries during search.
Add apt install instructions for clang, lld, llvm, and nsis to README Ubuntu-to-Windows build section. Add clang-cl availability check to cargo-xwin wrapper script with helpful error message directing users to install LLVM/Clang toolchain when missing.
Add cargo-xwin wrapper script that invokes `cargo xwin` subcommand and update Linux Windows build script to use wrapper as --runner instead of cargo-xwin binary name directly. Add chmod +x to ensure wrapper is executable before build.
