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 Visio.md

@@ -0,0 +1,14 @@
+[[Blue:Licensed]]
+
+# Microsoft Visio
+
+Visio Plan 2 is licensed per user in Microsoft 365.
+
+## Install
+1. Confirm the user has a Visio license assigned (Microsoft 365 admin center).
+2. Software Center > **Microsoft Visio - en-us**.
+3. Open Visio > **File > Account** and confirm the product is activated.
+
+## Notes
+- Visio installs alongside Microsoft 365 Apps and must use the same channel (Current/Monthly Enterprise) or the install will fail.
+- Custom stencils: `Documents\My Shapes`. USMT migrates these with the Documents folder.