Infra: provision a Windows test VM on Proxmox for agent + winget end-to-end testing

[ChrisonSimtian]

Why

Several things can only be validated on a real Windows machine, and we don't have one in the loop today:

• winget install — bootstrapping/validating ErpForFactoryGames.Agent (Agent: bootstrap ErpForFactoryGames.Agent into winget-pkgs so winget install works #298) requires a Windows box (winget validate --manifest, winget install --manifest, wingetcreate submit).
• Agent Windows service — erp-agent --install registers a Windows service, the erp-agent:// URL-protocol handler, and seeds %ProgramData%\ErpForFactoryGames\agent.json. None of that path is exercisable from Mac/Linux.
• Cross-machine hosted topology — the agent-first onboarding work (Setup wizard: first step should be agent install + pair (hosted mode) #268/PathPickerDialog enumerates the webapp's filesystem, not the agent's #270, PR fix(web): agent-first onboarding + hydration-race fix (#260 #268 #269 #270) #297) assumes the agent runs on a different machine than the server and dials out. A persistent Windows VM lets us test that real boundary (pair → agent uploads Docs.json → planner loads) instead of mocking it.
• Future MSI (Agent: Windows MSI installer #219) — installer testing needs Windows too.

It also removes the "turn my laptop on" dependency for manual agent testing.

Scope

• Provision a Windows VM on Proxmox (Win 11 or Server; sized for Satisfactory dedicated/save-folder simulation isn't required — we only need the agent + a Docs.json).
• Install winget + wingetcreate; verify winget install --manifest src\Agent\packaging\winget\ works against a local build.
• Install the agent as a Windows service end-to-end; confirm --install, pairing via erp-agent:// deep link, and catalogue/save upload to a server instance.
• Document the VM (access, snapshot baseline, how to reset) so it's a repeatable test fixture, not a pet.
• (Stretch) Evaluate whether it can act as a self-hosted GitHub Actions runner for the Windows legs of release-images.yml / ui-tests.yml, or at least an on-demand manual-test target.

Notes

Unblocks the manual half of #298 (winget bootstrap). Related: #299 (macOS/brew — separate platform), #219 (MSI).

[ChrisonSimtian]

Provisioning work tracked in the homelab repo: Chrison-Homelab/Homelab#26 (BL-014). The actual VM lives there; this issue stays as the ERP-side tracker for what the VM unblocks (#219/#301 MSI, #298 winget bootstrap, #268/#270 cross-machine agent).