No mass import capability

Need a way for people migrating from other similar services to mass import their notes.
Should provide a way/format(s) for importing a mass of notes and including some meta field to also capture pre-existing tags.

The issue does not name files, tests, an import entry point, or supported source formats. Start by locating the macOS note-import and tag-handling flows, then clarify which formats and metadata must be supported. Done should include a defined mass-import workflow that preserves pre-existing tags and has coverage for the agreed formats.

Written by the indexing model from the issue text.