fix: Windows path support, error handling, and dedup in validators

- session-manager.js: fix getSessionStats path detection to handle
  Windows paths (C:\...) in addition to Unix paths (/)
- package-manager.js: add try-catch to setPreferredPackageManager for
  consistent error handling with setProjectPackageManager
- validate-hooks.js: extract duplicated hook entry validation into
  reusable validateHookEntry() helper
- Update .d.ts JSDoc for both fixes

scripts/lib/package-manager.js

@@ -246,7 +246,12 @@ function setPreferredPackageManager(pmName) {
   const config = loadConfig() || {};
   config.packageManager = pmName;
   config.setAt = new Date().toISOString();
-  saveConfig(config);
+
+  try {
+    saveConfig(config);
+  } catch (err) {
+    throw new Error(`Failed to save package manager preference: ${err.message}`);
+  }
 
   return config;
 }