fix(batch): resolve pandoc path handling and include-subfolders option

- Normalize pandoc command parsing with path.basename() to support bundled binary paths
- Use bundled pandoc binary in convertWithPandoc instead of relying on PATH
- Forward includeSubfolders checkbox state from renderer to main process
- Add pandoc availability check before batch conversion
- Re-enable Start button when batch conversion completes
- Clean up obsolete dist build artifact causing test snapshot warning
- Bump version to 4.4.4

src/plugins/settings-store.js

@@ -14,7 +14,7 @@ class SettingsStore {
     this.backend.set(key, value);
   }
 
-  onChanged(key, callback) {
+  onChanged(_key, _callback) {
     // Deferred: plugins read settings on init/activate for MVP.
     // Full change notification requires IPC watcher in main process.
   }