Add error reporting

# Goal
At the moment, when a user uploads an AOI there's absolutely no way to know if it's failed. The only indicator of success is if an MBTiles file appears, and even then there's no way to know if the file is correct other than to download it and try it out.

Ideally a user would see a failure notice of some kind if something goes wrong. Even better would be an indication of the time remaining for a file to be processed.

# Tasks
- Wire up some logging from the TileHuria app itself
- Create some user-friendly error messages
- Hook them to the Status slot in the MBTiles page

Start by tracing AOI upload processing in the TileHuria app and the Status slot in the MBTiles page. Determine how failures and processing progress are currently represented, then define the user-facing error and progress behavior from the listed tasks. Done means upload failures are visible, messages are understandable, and status is connected to the MBTiles page.

Written by the indexing model from the issue text.