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/Install-VeeamCollector.ps1

@@ -22,7 +22,7 @@ param(
     [Parameter(Mandatory)][string]$ApiUrl,
     [Parameter(Mandatory)][string]$Tenant,
     [string]$SourceSystem = 'Veeam B&R',
-    [ValidateRange(5, 1440)][int]$IntervalMinutes = 15,
+    [ValidateRange(5, 1440)][int]$IntervalMinutes = 60,
     [ValidateRange(1, 720)][int]$LookbackHours = 48,
     [string]$InstallDir = (Join-Path $env:ProgramFiles 'BackupDashboard'),
     # Defaults to the machine-wide PowerShell 7 install