fix: Windows needs .exe suffix for xlings and ninja binary paths

cfg.xlingsBinary was set to "registry/bin/xlings" without .exe,
causing cmd.exe to fail with "not recognized as an internal or
external command". Also fix ninja marker check.

Author: Sunrisepeak

src/config.cppm

@@ -441,7 +441,11 @@ std::expected<GlobalConfig, ConfigError> load_or_init(
     // <XLINGS_HOME>/bin/xlings, which satisfies xlings's own shim-
     // creation guard (`if fs::exists(homeDir/"bin"/"xlings")`),
     // making ensure_sandbox_xlings_binary() a no-op.
+#if defined(_WIN32)
+    cfg.xlingsBinary  = cfg.registryDir / "bin" / "xlings.exe";
+#else
     cfg.xlingsBinary  = cfg.registryDir / "bin" / "xlings";
+#endif
     cfg.bmiCacheDir   = cfg.mcppHome / "bmi";
     cfg.metaCacheDir  = cfg.mcppHome / "cache";
     cfg.logDir        = cfg.mcppHome / "log";

src/xlings.cppm

@@ -834,7 +834,11 @@ void ensure_ninja(const Env& env, bool quiet,
     if (std::filesystem::exists(root)) {
         std::error_code ec;
         for (auto& v : std::filesystem::directory_iterator(root, ec)) {
+#if defined(_WIN32)
+            if (std::filesystem::exists(v.path() / "ninja.exe")) return;
+#else
             if (std::filesystem::exists(v.path() / "ninja")) return;
+#endif
         }
     }
     if (!quiet)