Newsletter: subscriber import and export (CSV)

[srmdn]

Problem

There is no way to bulk-add existing subscribers or back them up. An author migrating from another platform (Substack, Ghost, Mailchimp) has no path to bring their list over.

Proposed solution

• GET /api/admin/subscribers/export — returns a CSV file (email,subscribed_at)
• POST /api/admin/subscribers/import — accepts a CSV upload, inserts new emails, skips duplicates, returns a summary ({ imported, skipped })
• Subscribers page: Export button + Import file input

Notes

• Import should be lenient: skip blank lines, skip invalid emails, skip duplicates silently
• No token is generated for imported subscribers until they interact (or generate on import — TBD)
• Keep within the scope freeze: do not add double opt-in here