post-connection-implement-relinkinglisted

# Implementing Relinking and Detailed Error Messaging ## Purpose Credentials expire, permissions get revoked, and admins change — relinking lets end users re-authenticate without contacting support. Detailed error messaging (rather than "something went wrong") tells users exactly what failed and who needs to fix it. ## Prerequisites - `post-connection-build-settings-page` complete - `/api/merge/relink-integration` endpoint working --- ## Before Proceeding Tell the user: "Implementing relinking requires storing error state on the `linked_accounts` table (an `error_category` column and optionally `error_detail`). I'll generate a migration for this. Ready to proceed?" Wait for confirmation before continuing. ## Part 1: Relinking Flow Prompt the codebase to implement relinking with multiple entry points and clean state management: > Implement relinking with the following requirements: > > **Entry points** — expose the reconnect action from at least two places: > - Settings page: always-visible "Reconnect" button > - Error banner CTA: "Reconnect" link surfaced when status is not active > - Email notification link (deep-link into the settings page reconnect flow) > > **Flow:** > 1. Call `POST /api/merge/relink-integration` to get a new link token > 2. Open Merge Link modal using that token > 3. On `onSuccess` callback: refresh integration status from DB and update UI > > **Success state:** Set `status = "active"` in `linked_accounts`, clear any stored error state (error