Document UTF-8 wrapper coverage against LuaJIT Windows import surface

[Copilot]

This PR addresses the request to verify whether additional patching is needed based on the current LuaJIT Windows import list.
Result: path/command/environment-sensitive imports are already covered by existing UTF-8 wrappers; no new wrapper hooks were introduced.

• What was reviewed

  • Compared the provided import list with the current wrapper layer (utf8_wrappers.c/.h).
  • Focused on APIs that consume ANSI path/command/env strings and can break with non-ASCII input.

• Coverage confirmed

  • Already wrapped and redirected:
    • fopen / freopen
    • remove
    • rename
    • _popen
    • system
    • getenv
    • GetModuleFileNameA
    • LoadLibraryExA

• What changed in this PR

  • Added an explicit Imported-symbol audit (Windows) section to README.md.
  • Documented why the remaining imported symbols do not need Unicode-path wrappers (math/runtime/threading/memory/descriptor-level APIs).

// Existing redirections already in place
#define fopen               fopen_utf8
#define remove              remove_utf8
#define rename              rename_utf8
#define _popen              popen_utf8
#define system              system_utf8
#define getenv              getenv_utf8
#define GetModuleFileNameA  GetModuleFileNameA_utf8
#define LoadLibraryExA      LoadLibraryExA_utf8

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