Feature Request: Database importer recovery on partial failure

Based on [this user's feedback](https://x.com/davidperezmk/status/2075101172231291262)

### What

A recovery mechanism for the database importer when the import process fails or stops midway through.

### Why

If the database import stops halfway, the user is left in a broken state with no clear way to recover. The site becomes stuck with a partially imported database. Currently users have to rely on the AI assistant to fix it.

### How

- Implement rollback on failure (restore the previous DB state).
- Or allow resuming the import from where it stopped.
- At minimum, provide clear error messaging and instructions to recover manually.

No files, tests, or importer entry points are named. Start by locating the database import flow and tracing how failures leave the site partially imported. Done means choosing and implementing a recovery path—rollback, resume, or documented manual recovery—with clear error messaging and coverage for an interrupted import.

Written by the indexing model from the issue text.