feat(ui): default pst_import_range_days in the settings fallback

src/lib/stores/settings.svelte.ts

@@ -43,6 +43,7 @@ const DEFAULT_SETTINGS: AppSettings = {
   retention_max_size_gb: null,
   pst_last_path: null,
   pst_auto_sync: false,
+  pst_import_range_days: null, // full mailbox history by default
   audio_output_device: null, // system default render device (FR-CAP-1)
   microphone_enabled: true, // capture the user's mic into the transcript (FR-CAP-7)
   audio_input_device: null, // system default capture device