fix: Import from Nextcloud Passwords stalls and never completes

[Roshan931]

Fixes #870

Root cause

Passwords App CSV importer maps non-existent columns, producing undefined values that abort import

Changes

• js/importers/importer-ocpasswords.js now reads the current Passwords app CSV columns (label, username, password, notes, url) with fallback to the legacy ocPasswords columns (website, fulladdress), never emits undefined field values, skips rows without a label, and the displayed export steps match the app's current "Backup or export -> Predefined CSV" flow.