Cross-posting: identity verification and reconnect reminders

[Adron]

Two gaps

1. POST /api/user/identities/verify — unimplemented. ConnectedAccountsViewModel reads link state from GET /api/user/identities (correctly — per CLAUDE.md, /api/auth/{provider}/status reports server configuration, not per-user link state). This endpoint presumably re-validates a stored credential; confirm what it does live before wiring it.

2. Integration reconnect reminders. Per /help/settings there is an Integration reconnect reminders setting, on by default: "InterlinedList reminds you when one of your cross-posting connections (such as LinkedIn) is expiring or needs reconnecting, so your cross-posts don't quietly stop." The app shows no such warning and does not expose the setting.

Acceptance criteria

• Behaviour of identities/verify established live and implemented if it is meaningful for a native client.
• An expiring/needs-reconnect credential is flagged in Connected Accounts with a reconnect action (browser handoff).
• The reminders preference is exposed wherever it lives (/api/user/update or notification preferences — confirm which).
• A cross-post that fails because a credential lapsed says so, rather than failing silently.