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)

docker-compose.yml

@@ -0,0 +1,13 @@
+# Coolify: create a "Docker Compose" resource pointing at this repository (or a
+# "Dockerfile" resource), and set the domain to port 8080.
+services:
+  usmt-dash:
+    build: .
+    image: usmt-dash:latest
+    init: true
+    restart: unless-stopped
+    environment:
+      - USMT_MODE=Demo
+      - TZ=UTC   # set your timezone, e.g. America/New_York
+    ports:
+      - "8080:8080"