fix(updater): Windows installs update from the Windows bundle, not the source tarball (#373)

[rowkav09]

Part of #373 (1 of 2: check + download).

What

• updateAssetName(version, platform): on win32 it's nowplaying-vX.Y.Z-windows-x64.zip (what release.yml publishes since ci(release): build and attach Windows installer and zip to stable releases (#353) #356). Anywhere else it stays nowplaying-vX.Y.Z.tar.gz.
• checkForUpdate takes platform (defaults to process.platform), picks that asset and returns assetName. A Windows install refuses a release that only has the tarball instead of falling back to it.
• downloadVerifiedUpdate checks the digest against the SHA256SUMS line for that exact asset. It only accepts the two names published for that version, so a bad assetName can't point it at something else. Without assetName it defaults to the tarball, as before.
• createAutoUpdater passes platform through.

Existing tests pin platform: "linux" so they mean the same thing on the Windows CI runner.

Tests

• New: Windows picks the zip, Linux picks the tar, a Windows install rejects a tarball-only release, name mapping, zip checksum line, unexpected names refused.
• Updater suites: 35 pass. Full npm test: only the existing local sharp-runtime failure (passes in CI).

Next PR: install unpacks and validates the Windows bundle, plus an end-to-end check -> download -> swap test.

[github-actions]

/mira pause

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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