gbrain import <single-file.md> imports 0 pages; pass a directory

With gbrain 0.44, gbrain import path/to/note.md on a new markdown file printed "Import complete: 0 pages imported, 0 skipped" and the page was not searchable. Importing the parent directory (gbrain import concepts) is the path that works; it skips unchanged files by content hash, but on a large folder it can still run past 5 minutes, so run it in the background. Unconfirmed whether newer gbrain versions accept single files.