B/better reports 2

[worldofjoni]

Second phase of better image report handling (#160), follow up to #164.

Contains:

• RESTful admin API under /admin with BASIC auth
• API endpoints to delete and verify images
• one-click buttons in report mail to delete/verify image

TODO

• [x] human-readable admin API response
• [ ] improve notification email for when image is deleted / verified (same content as report mail?)
• [x] tests for database access
• [x] test for image file deletion
• [x] test for command
• [x] maybe tests for admin API?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.48276% with 8 lines in your changes missing coverage. Please review.

Project coverage is 92.72%. Comparing base (fcab00e) to head (0723790).

Files	Patch %	Lines
backend/src/interface/api_command.rs	80.00%	6 Missing :warning:
backend/src/layer/data/mail/mail_sender.rs	97.05%	1 Missing :warning:
backend/src/layer/trigger/api/bin.rs	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #166 +/- ## ========================================== + Coverage 92.56% 92.72% +0.15% ========================================== Files 39 41 +2 Lines 1615 1746 +131 ========================================== + Hits 1495 1619 +124 - Misses 120 127 +7 ```

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