Phase 0 of the file-based storage plan (docs/plans/
2026-06-24-file-based-storage.md). Foundation only — no editor or
DB change yet.
- VaultService (SharedPreferences): stores the vault root path,
vaultRootValid() = path set AND directory exists.
- VaultSetupScreen: first-run folder picker (file_picker, Windows).
- main.dart gates HomeScreen behind a valid vault, re-prompting if
the saved folder is gone.
- Settings: a Vault section to change the folder.
Editors still use SQLite; later phases move annotations into
per-file sidecars under the vault. analyze clean, tests green.
