Generalize USMT Dash and add a containerized demo mode

Remove all environment-specific data and make the dashboard adoptable
anywhere, then add a demo that runs the real PowerShell services.

- Strip cached device data, internal knowledge-base articles and
  screenshots, server/site names and the old project notes; replace the
  knowledge base with generic sample articles and diagrams
- Move every environment value into Config/usmt-dash.psd1
- Route all infrastructure access in the worker and Get-Software.ps1
  through a provider (Providers/SCCM.ps1), with a config-driven asset
  inventory view instead of a hard-coded custom class
- Add Providers/Demo.ps1: a deterministic simulated fleet whose
  migrations progress in real time, and Demo/New-DemoData.ps1 to seed it
- Server: -Demo makes the API read-only; add get-config and get-logs;
  serve static files only from web/, Documentation/ and an allowlist of
  Data/ files with a path-traversal guard; gzip large responses
- Mirror both services' console output to Data/Logs via a Write-Host
  proxy, and add a terminal panel to the dashboard that streams it
- Demo sandbox (web/demo/demo.js): visitor changes to tags, articles and
  images are kept in the visitor's browser and echoed in the terminals;
  nothing a visitor does reaches the server
- Vendor marked, highlight.js and html2pdf.js instead of loading CDNs
- Dockerfile and compose file for hosting the demo (Coolify-ready)

Documentation/Microsoft Power BI.md

@@ -0,0 +1,12 @@
+[[Gray:Optional]]
+
+# Microsoft Power BI
+
+## Install
+- Software Center > **Microsoft Power BI Desktop (x64)**.
+- Sign in with the user's company account to publish to the Power BI service.
+
+## Notes
+- `.pbix` reports are usually in OneDrive or SharePoint, so nothing to migrate locally.
+- **Power Pivot for Excel** is grouped with Power BI in the software view. It's enabled from Excel > File > Options > Add-ins > COM Add-ins.
+- Gateways (on-premises data gateway) are installed on servers, **never** on user workstations.