Fix dependency installation broken on Windows

[matthewp]

Changes

• Fixes npm create astro@latest failing to install dependencies on Windows since 5.0.1. The 5.0.1 change removed shell: true from spawn() to avoid DEP0190 warnings and attempted to handle Windows by appending .cmd to package manager names (e.g. npm → npm.cmd). However, .cmd files on Windows cannot be spawned directly without a shell — the Node.js docs explicitly state this. The fix now routes known package manager shims through cmd.exe /d /s /c <name>.cmd on Windows, which is the correct way to invoke them without shell: true.
• Fixes the error [object Object] message that appeared when installation failed. The catch block was throwing a plain object { stdout, stderr, exitCode: 1 } instead of an Error, which stringified as [object Object] in the UI. It now throws a proper Error with the actual message.

Testing

• All 116 existing create-astro tests pass. The Windows-specific spawn path is not unit-testable in CI (Linux/macOS), but the logic mirrors the approach documented in the Node.js child_process docs for invoking .cmd/.bat files without a shell.
• Manually confirmed by the reporter that 5.0.0 worked and 5.0.1 did not — the root cause matches exactly: 5.0.1 introduced the broken .cmd direct-spawn approach.

Docs

No docs update needed — this is a bug fix in the CLI scaffolding tool with no user-facing API changes.

[changeset-bot]

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Latest commit: e9af638

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[pkg-pr-new]

npm i https://pkg.pr.new/create-astro@16106

commit: e9af638