Repair files broken by the web-UI merge

The merge of add-backend-api into main committed unresolved conflicts
and corrupted uploads; the API could not import on main.

- backend/app/settings.py, deploy/backup-dashboard-api.service,
  collectors/veeam/README.md: remove conflict markers, restoring the
  add-backend-api versions
- backend/app/__init__.py, backend/tests/__init__.py: were 1024 null
  bytes ("source code string cannot contain null bytes"); now empty
- Remove the accidental Backup-Dashboard gitlink at the repo root and a
  duplicate collectors/veeam/MockVeeam.ps1 (identical to tests/)
- Restore the 60-minute collector interval from 17ee303, which the
  merge reverted to 15, and update the docs to match

Co-Authored-By: Claude Opus 5.5 <[email protected]>

collectors/veeam/Send-VeeamBackupStatus.ps1

@@ -3,7 +3,7 @@
     Reports Veeam Backup & Replication job results to the Backup Dashboard.
 
 .DESCRIPTION
-    Runs on the VBR server, normally as a SYSTEM scheduled task every 15 minutes
+    Runs on the VBR server, normally as a SYSTEM scheduled task every 60 minutes
     (see Install-VeeamCollector.ps1). For every backup, replica and backup copy job it sends:
       - the job's next scheduled run (drives the dashboard's Overdue flag), and
       - every session from the last LookbackHours that the dashboard hasn't already received