Adds an "unlisted" flag on episodes rather than reusing the existing
hard-delete route, since a hard delete cascades to purchases/earnings
(ON DELETE CASCADE) and would wipe a producer's sales history and any
unwithdrawn earnings for that episode. Unlisting only affects feed.xml
output — the episode, its purchases, and reseller listings all stay
intact and it can be relisted at any time.
Wires up the missing frontend for it too: the podcast settings page
had no episode list or management controls at all before this, despite
the backend already exposing full episode CRUD.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>