fix(websearch): use 'where' command on Windows for CLI detection

Fixes #273

The websearch-transformer hook used hardcoded 'which' command which doesn't
exist on Windows. Now uses process.platform detection to choose 'where' on
Windows and 'which' on Unix systems.

lib/hooks/websearch-transformer.cjs

@@ -154,7 +154,10 @@ process.stdin.on('error', () => {
  */
 function isCliAvailable(cmd) {
   try {
-    const result = spawnSync('which', [cmd], {
+    const isWindows = process.platform === 'win32';
+    const whichCmd = isWindows ? 'where.exe' : 'which';
+
+    const result = spawnSync(whichCmd, [cmd], {
       encoding: 'utf8',
       timeout: 2000,
       stdio: ['pipe', 'pipe', 'pipe'],