Add Azure Backup (MARS agent) collector

PowerShell script for servers running the MARS agent, run as a SYSTEM
scheduled task (hourly) under Windows PowerShell 5.1, which the
agent's MSOnlineBackup module targets. Each server is one dashboard job.

- Backup jobs from Get-OBJob (in progress and -Previous) within the
  lookback window; restores are ignored. Completed with failed bytes
  or an error reports as warning
- Next run computed from the backup and System State policy schedules;
  left empty for every-N-weeks schedules to avoid false Overdue alarms
- Property reads tolerate unknown names, since the agent's object
  model isn't documented; Get-MarsCollectorDiagnostics.ps1 dumps the
  real structure for checking
- Install-MarsCollector.ps1 mirrors the Veeam installer; tests/MockMars.ps1
  provides stand-in cmdlets

Not yet run against a real MARS agent.

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

collectors/mars/README.md

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+# Azure Backup (MARS agent) collector
+
+A PowerShell script that runs on each server with the Microsoft Azure Recovery Services (MARS)
+agent and reports its backups to the dashboard. Each server appears as one job,
+named `<SERVER> - Azure Backup` by default.
+
+> **Not yet checked against a real MARS agent.** The cmdlets are the agent's own (`Get-OBJob`,
+> `Get-OBPolicy`, `Get-OBSchedule`), but the property names of the objects they return aren't
+> documented. Before installing on the first server, run `Get-MarsCollectorDiagnostics.ps1` and
+> the collector with `-DryRun` (see below) to confirm what it reads.
+
+## Install (on the server, as an administrator)
+
+Runs under Windows PowerShell 5.1 (`powershell.exe`), which the agent's `MSOnlineBackup` module
+targets and which every supported Windows Server has.
+
+1. On the dashboard host, create a key for this server:
+   ```bash
+   python manage.py create-key mars-acme-fs01
+   ```
+2. Copy this folder to the server and run:
+   ```powershell
+   .\Install-MarsCollector.ps1 -ApiUrl https://backups.example.com -Tenant "Acme Corp"
+   ```
+   Add `-JobName "File Server"` to choose the name shown on the dashboard. It prompts for the
+   key, then:
+   - writes `C:\ProgramData\BackupDashboard\mars-collector.json` (readable only by SYSTEM and Administrators)
+   - copies the script to `C:\Program Files\BackupDashboard\`
+   - registers the scheduled task **Backup Dashboard - MARS collector** (SYSTEM, every 60 minutes)
+3. Preview the payloads, then backfill 30 days so the history view is populated straight away:
+   ```powershell
+   powershell.exe -File 'C:\Program Files\BackupDashboard\Send-MarsBackupStatus.ps1' -DryRun
+   powershell.exe -File 'C:\Program Files\BackupDashboard\Send-MarsBackupStatus.ps1' -LookbackHours 720
+   ```
+
+It can be installed alongside the Veeam collector: it uses its own config, state, log and task.
+Re-run the installer to change settings or update the script.
+
+## What it sends
+
+| Dashboard | MARS |
+|---|---|
+| Company | `Tenant` from the config |
+| Job | One per server, ID `mars:<computer name>`, so changing `JobName` renames rather than duplicates it |
+| Status | Backup job state: Failed → **Failed**. Completed with failed bytes or an error → **Warning**. Aborted/cancelled or unrecognised → **Warning**. In progress → **Running**. Restore jobs are ignored |
+| Started / finished | Job start / end time |
+| Next scheduled | Next slot from the backup policy schedule, or the System State policy's if that's sooner. Empty (so never Overdue) for schedules that run every 2+ weeks, since which week is next can't be told |
+| Message | Job and per-datasource errors, and datasources with failed bytes |
+| Size | Bytes transferred, summed across datasources |
+
+Each run covers the last 48 hours (`LookbackHours`). Jobs already delivered are recorded in
+`mars-collector.state.json`.
+
+## Troubleshooting
+
+- Log: `C:\ProgramData\BackupDashboard\mars-collector.log`. Exit codes: `0` OK, `1` some runs
+  failed to send (retried next run), `2` setup failed (config or MARS module).
+- Wrong status, sizes or messages: run `.\Get-MarsCollectorDiagnostics.ps1` (read-only). It prints
+  the real structure of the objects the agent's cmdlets return.
+
+## Testing without MARS
+
+```powershell
+. ./tests/MockMars.ps1
+./Send-MarsBackupStatus.ps1 -ConfigPath ./my-test-config.json -DryRun
+```