feat(desktop): add Windows build machines like Linux ones

[janicduplessis]

Description

Depends on #3653 (stack: #3610 -> #3618 -> #3621 -> #3631 -> #3638 -> #3639 -> #3647 -> #3653 -> this).

Windows machines can now take offloaded Android builds (#3640) and run stim-server service and stim-server setup --build as a per-user scheduled task (#3658). Stim Desktop still left them out:

• The Add Remote Machine wizard listed only macOS and Linux tailnet peers.
• The build tips, the Machine page empty state and the build suggestions did not count Windows peers.
• A Windows row still showed the Simulators enabled toggle.

Solution

A Windows peer (Tailscale OS: "windows") gets the same treatment as a Linux one. TailnetOS gains windows, and the Linux-only branches now key on "not macOS" (buildsAndroidOnly). Setup-related functions take the peer's TailnetOS instead of a Linux flag.

For a Windows peer, the wizard:

• Pick: lists it as Windows · Android builds only. The empty tailnet state also links the Windows Tailscale download.
• What it does: offers Builds only; Hosted simulators is disabled because it needs a Mac.
• Set it up:
  • The command is PowerShell and runs npx.cmd. Plain npx resolves to npm's npx.ps1, which the default script execution policy on Windows desktops (Restricted) blocks.
  • A backtick continues each line and the package is quoted. Without the quotes, PowerShell reads the leading @ of @stim-cli/server@… as its splatting operator.
  • It has no sudo or linger.
  • The text says PowerShell. The footnote says no administrator rights are needed and gives the --path-prepend remedy for a version manager's node.exe shim, as feat: run stim-server service and setup on Windows #3658 documents.
  • The preview and mirror say "scheduled task running" and hide the Apple tool lines.
• Tools: judges Android only.
• Test build: builds Android.

Outside the wizard, the remote machine tip, the Machine page empty state, and the new-peer and build-slot suggestions count Windows peers. A Windows row hides the Simulators toggle. The hosted-simulators tip and the device-limit suggestion stay Mac-only.

The CLI rules from #3639 and #3653 already key on "not macOS" (doctor's device-host ask, cannotHost, the device pool and hosting candidates). This PR adds Windows cases to their tests.

The generated npx --package "@stim-cli/server@<version>" command works on Windows only once a published server release includes #3658, which lives on its own branch off #3631.

Test plan

Fixture renders, and a real windows-latest runner on the tailnet as stim-windows-wizard, prepared from #3658's branch through a throwaway branch's windows-debug.yml.

This MacBook's screen was locked, so I drove AddMachineModel with its production dependencies from an uncommitted XCTest harness: real tailscale status, the HTTPS journal probe, this branch's CLI, and a scratch STIM_HOME.

• The pick list showed stim-windows-wizard (and another agent's stim-windows-paths) as Windows peers. Picking it set Builds only.
• The generated command, run in PowerShell over SSH:
  • I replaced npx --package with feat: run stim-server service and setup on Windows #3658's built server and added --yes, because npm has no release with Windows setup. The backtick continuation parsed.
  • Setup reused the scheduled task I had installed from that build, reused the route, and approved the build request. The wizard read every journal step.
  • stim-server devices listed only the build request, so no device-host request was sent.
  • Separately, npx --yes --package "@stim-cli/server@1.20.2" stim-server --version printed 1.20.2 in PowerShell, so the quoted form parses. The runner's command used npx, not npx.cmd; the switch to npx.cmd came after the runner was stopped, and it rests on npm installing npx.cmd next to npx.ps1.
• Tools showed only the Stim build and Android rows. Stim build blocked, because the runner ran feat: run stim-server service and setup on Windows #3658's build and this Mac ran this branch. That mismatch also rules out a real test build here: this stack has neither feat: let Windows machines take offloaded Android builds #3640's Windows worker nor feat: run stim-server service and setup on Windows #3658.

Pick (real)	What it does (real)

Set it up (real)	Tools (real)

Pick (fixture)	What it does (fixture)	Set it up (fixture)

The real "Set it up" capture predates the mirror's "waiting for approval in PowerShell" wording, which a unit test covers.

Unit tests cover:

• the Windows command, preview and mirror lines, and capability forcing;
• peers: Windows in, other systems out, macs unchanged;
• the model's Android-only Tools and command for Linux and Windows;
• the CLI's pool validation and hosting candidates for a windows peer.

Fixes #3659