Add `_seed_root_symlink_mappings` method to ensure symlinked root folders are recorded before deep scanning, preventing them from being missed during directory traversal. This ensures that root symlinks are properly captured in the path mappings.
Additionally, normalize separators in relative paths for cross-platform consistency in `BaseModelService`, and update tests to verify root symlinks are preserved in the cache.
- Added threading import and optional `_rescan_thread` for background operations
- Simplified `_load_symlink_cache` to only validate path mappings, removing fingerprint checks
- Updated `_initialize_symlink_mappings` to rebuild preview roots and schedule rescan when cache is loaded
- Added `_schedule_symlink_rescan` method to perform background validation of symlinks
- Cleared `_path_mappings` at start of `_scan_symbolic_links` to prevent stale entries
- Background rescan improves performance by deferring symlink validation after cache load